Publications

@article{Wolf2023,

title = {Efficient site-resolved imaging and spin-state detection in dynamic two-dimensional ion crystals},

author = {Robert N. Wolf and Joseph H. Pham and Julian Y. Z. Jee and Alexander Rischka and Michael J. Biercuk},

year  = {2023},

date = {2023-03-01},

abstract = {Resolving the locations and discriminating the spin states of individual trapped ions with high fidelity is critical for a large class of applications in quantum computing, simulation, and sensing. We report on a method for high-fidelity state discrimination in large two-dimensional (2D) crystals with over 100 trapped ions in a single trapping region, combining a novel hardware detector and an artificial neural network. A high-data-rate, spatially resolving, single-photon sensitive timestamping detector performs efficient single-shot detection of 2D crystals in a Penning trap, exhibiting rotation at about $25,mathrmkHz$. We then train an artificial neural network to process the fluorescence photon data in the rest frame of the rotating crystal in order to identify ion locations with a precision of $~90%$, accounting for substantial illumination inhomogeneity across the crystal. Finally, employing a time-binned state detection method, we arrive at an average spin-state detection fidelity of $94(1)%$. This technique can be used to analyze spatial and temporal correlations in arrays of hundreds of trapped-ion qubits.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Becher2023,

title = {Rare Earth Ions for Optical Quantum Technologies, Section 3, 2023 roadmap for materials for quantum technologies},

author = {Christoph Becher and Weibo Gao and Swastik Kar and Christian D Marciniak and Thomas Monz and J. G. Bartholomew and Philippe Goldner and Huanqian Loh and Elizabeth Marcellina and Kuan Eng Johnson Goh and Teck Seng Koh and Bent Weber and Zhao Mu and Jeng-Yuan Tsai and Qimin Yan and Tobias Huber-Loyola and Sven Höfling and Samuel Gyger and Stephan Steinhauer and Val Zwiller},

url = {http://arxiv.org/abs/2012.13408 http://dx.doi.org/10.1103/PhysRevLett.127.040503 https://link.aps.org/doi/10.1103/PhysRevLett.127.040503},

doi = {10.1088/2633-4356/aca3f2},

issn = {2633-4356},

year  = {2023},

date = {2023-03-01},

journal = {Materials for Quantum Technology},

volume = {3},

number = {1},

pages = {012501},

abstract = {Quantum technologies are poised to move the foundational principles of quantum physics to the forefront of applications. This roadmap identifies some of the key challenges and provides insights on material innovations underlying a range of exciting quantum technology frontiers. Over the past decades, hardware platforms enabling different quantum technologies have reached varying levels of maturity. This has allowed for first proof-of-principle demonstrations of quantum supremacy, for example quantum computers surpassing their classical counterparts, quantum communication with reliable security guaranteed by laws of quantum mechanics, and quantum sensors uniting the advantages of high sensitivity, high spatial resolution, and small footprints. In all cases, however, advancing these technologies to the next level of applications in relevant environments requires further development and innovations in the underlying materials. From a wealth of hardware platforms, we select representative and promising material systems in currently investigated quantum technologies. These include both the inherent quantum bit systems and materials playing supportive or enabling roles, and cover trapped ions, neutral atom arrays, rare earth ion systems, donors in silicon, color centers and defects in wide-band gap materials, two-dimensional materials and superconducting materials for single-photon detectors. Advancing these materials frontiers will require innovations from a diverse community of scientific expertise, and hence this roadmap will be of interest to a broad spectrum of disciplines.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rochman2023,

title = {Microwave-to-optical transduction with erbium ions coupled to planar photonic and superconducting resonators},

author = {Jake Rochman and Tian Xie and J. G. Bartholomew and K. C. Schwab and Andrei Faraon},

url = {https://www.nature.com/articles/s41467-023-36799-0},

doi = {10.1038/s41467-023-36799-0},

issn = {2041-1723},

year  = {2023},

date = {2023-03-01},

journal = {Nature Communications},

volume = {14},

number = {1},

pages = {1153},

abstract = {Optical quantum networks can connect distant quantum processors to enable secure quantum communication and distributed quantum computing. Superconducting qubits are a leading technology for quantum information processing but cannot couple to long-distance optical networks without an efficient, coherent, and low noise interface between microwave and optical photons. Here, we demonstrate a microwave-to-optical transducer using an ensemble of erbium ions that is simultaneously coupled to a superconducting microwave resonator and a nanophotonic optical resonator. The coherent atomic transitions of the ions mediate the frequency conversion from microwave photons to optical photons and using photon counting we observed device conversion efficiency approaching 10 −7 . With pulsed operation at a low duty cycle, the device maintained a spin temperature below 100 mK and microwave resonator heating of less than 0.15 quanta.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Berkman2023,

title = {Observing Er3+ Sites in Si With an In Situ Single-Photon Detector},

author = {Ian R Berkman and Alexey Lyasota and Gabriele G. Boo and J. G. Bartholomew and Brett C Johnson and Jeffrey C. McCallum and Bin-Bin Xu and Shouyi Xie and Rose L Ahlefeldt and Matthew J Sellars and Chunming Yin and Sven Rogge},

url = {https://link.aps.org/doi/10.1103/PhysRevApplied.19.014037},

doi = {10.1103/PhysRevApplied.19.014037},

issn = {2331-7019},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

journal = {Physical Review Applied},

volume = {19},

number = {1},

pages = {014037},

abstract = {We present a flexible method to study the optical properties of an Er 3+ ensemble in Si accessed via resonant excitation and in situ single-photon detection. The technique allows an efficient resonant pho-toluminescence detection of optically active centers with weak oscillator strength in transparent crystals without the need for nanofabrication on the sample. We observe 70 Er 3+ resonances in Si, of which 62 resonances have not been observed in the literature, with optical lifetimes ranging from 0.5 to 1.5 ms. We observe inhomogeneous broadening of less than 400 MHz and an upper bound on the homogeneous linewidth of 0.75 and 1.4 MHz for two separate resonances. These narrow, stable resonances confirm Er 3+ in Si as a promising quantum information candidate. We discuss the use of this technique for rapid characterization of future samples, with the aim of enhancing the prevalence of sites which are favorable for quantum information applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{kass2023rf,

title = {An rf Quantum Capacitance Parametric Amplifier},

author = {A El Kass and CT Jin and JD Watson and GC Gardner and S Fallahi and MJ Manfra and DJ Reilly},

year  = {2023},

date = {2023-01-01},

journal = {arXiv preprint arXiv:2304.13227},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Valahu2022,

title = {Direct observation of geometric phase in dynamics around a conical intersection},

author = {Christophe H. Valahu and Vanessa C. Olaya-Agudelo and Ryan J. MacDonell and Tomas Navickas and Arjun D. Rao and Maverick J. Millican and Juan B. Pérez-Sánchez and Joel Yuen-Zhou and Michael J. Biercuk and Cornelius Hempel and Ting Rei Tan and Ivan Kassal},

year  = {2022},

date = {2022-11-01},

abstract = {Conical intersections are ubiquitous in chemistry, often governing processes such as light harvesting, vision, photocatalysis, and chemical reactivity. They act as funnels between electronic states of molecules, allowing rapid and efficient relaxation during chemical dynamics. In addition, when a reaction path encircles a conical intersection, the molecular wavefunction experiences a geometric phase, which affects the outcome of the reaction through quantum-mechanical interference. Past experiments have measured indirect signatures of geometric phases in scattering patterns and spectroscopic observables, but there has been no direct observation of the underlying wavepacket interference. Here, we experimentally observe geometric-phase interference in the dynamics of a nuclear wavepacket travelling around an engineered conical intersection in a programmable trapped-ion quantum simulator. To achieve this, we develop a new technique to reconstruct the two-dimensional wavepacket densities of a trapped ion. Experiments agree with the theoretical model, demonstrating the ability of analog quantum simulators -- such as those realised using trapped ions -- to accurately describe nuclear quantum effects. These results demonstrate a path to deploying analog quantum simulators for solving some of the most difficult problems in chemical dynamics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{MacDonell2022,

title = {Predicting molecular vibronic spectra using time-domain analog quantum simulation},

author = {Ryan J. MacDonell and Tomas Navickas and Tim F. Wohlers-Reichel and Christophe H. Valahu and Arjun D. Rao and Maverick J. Millican and Michael A. Currington and Michael J. Biercuk and Ting Rei Tan and Cornelius Hempel and Ivan Kassal},

year  = {2022},

date = {2022-09-01},

abstract = {Spectroscopy is one of the most accurate probes of the molecular world. However, predicting molecular spectra accurately is computationally difficult because of the presence of entanglement between electronic and nuclear degrees of freedom. Although quantum computers promise to reduce this computational cost, existing quantum approaches rely on combining signals from individual eigenstates, an approach that is difficult to scale because the number of eigenstates grows exponentially with molecule size. Here, we introduce a method for scalable analog quantum simulation of molecular spectroscopy, by performing simulations in the time domain. Our approach can treat more complicated molecular models than previous ones, requires fewer approximations, and can be extended to open quantum systems with minimal overhead. We present a direct mapping of the underlying problem of time-domain simulation of molecular spectra to the degrees of freedom and control fields available in a trapped-ion quantum simulator. We experimentally demonstrate our algorithm on a trapped-ion device, exploiting both intrinsic electronic and motional degrees of freedom, showing excellent quantitative agreement for a single-mode vibronic photoelectron spectrum of SO$_2$.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{PhysRevResearch.4.033229,

title = {Doppler and sympathetic cooling for the investigation of short-lived radioactive ions},

author = {S. Sels and F. M. Maier and M. Au and P. Fischer and C. Kanitz and V. Lagaki and S. Lechner and E. Leistenschneider and D. Leimbach and E. M. Lykiardopoulou and A. A. Kwiatkowski and T. Manovitz and Y. N. Vila Gracia and G. Neyens and P. Plattner and S. Rothe and L. Schweikhard and M. Vilen and R. N. Wolf and S. Malbrunot-Ettenauer},

url = {https://link.aps.org/doi/10.1103/PhysRevResearch.4.033229},

doi = {10.1103/PhysRevResearch.4.033229},

year  = {2022},

date = {2022-09-01},

journal = {Phys. Rev. Res.},

volume = {4},

issue = {3},

pages = {033229},

publisher = {American Physical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{vigneau2022probing,

title = {Probing quantum devices with radio-frequency reflectometry},

author = {Florian Vigneau and Federico Fedele and Anasua Chatterjee and David Reilly and Ferdinand Kuemmeth and Fernando Gonzalez-Zalba and Edward Laird and Natalia Ares},

year  = {2022},

date = {2022-01-01},

journal = {arXiv preprint arXiv:2202.10516},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{aghaee2022inas,

title = {InAs-Al hybrid devices passing the topological gap protocol},

author = {Morteza Aghaee and Arun Akkala and Zulfi Alam and Rizwan Ali and Alejandro Alcaraz Ramirez and Mariusz Andrzejczuk and Andrey E Antipov and Mikhail Astafev and Bela Bauer and Jonathan Becker and others},

year  = {2022},

date = {2022-01-01},

journal = {arXiv preprint arXiv:2207.02472},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{harlech2022local,

title = {Local and Non-local Microwave Impedance of a Three-Terminal Hybrid Device},

author = {B Harlech-Jones and SJ Waddy and JDS Witt and D Govender and L Casparis and E Martinez and R Kallaher and S Gronin and G Gardner and MJ Manfra and others},

year  = {2022},

date = {2022-01-01},

journal = {arXiv preprint arXiv:2207.12516},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000680425800011,

title = {Precision characterization of the D-2(5/2) state and the quadratic 

 Zeeman coefficient in Yb-171(+)},

author = {T. R. Tan and C. L. Edmunds and A. R. Milne and M. J. Biercuk and C. Hempel},

doi = {10.1103/PhysRevA.104.L010802},

issn = {2469-9926},

year  = {2021},

date = {2021-07-01},

journal = {PHYSICAL REVIEW A},

volume = {104},

number = {1},

abstract = {We report measurements of the branching fraction, hyperfine constant, 

 and second-order Zeeman coefficient of the D-5/2 level in Yb-171(+) with 

 up to a two-orders-of-magnitude reduction in uncertainty compared to 

 previously reported values. We estimate the electric quadrupole reduced 

 matrix element of the S-1/2 <-> D-5/2 transition to be 12.5(4) ea(0)(2). 

 Furthermore, we determine the transition frequency of the F-7/2 <-> 

 D-1[3/2](3/2) at 760 nm with a similar to 25-fold improvement in 

 uncertainty. These measurements provide benchmarks for quantum-many-body 

 atomic-physics calculations and provide valuable data for efforts to 

 improve quantum information processors based on Yb-171(+).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000675546200005,

title = {Scalable hyperfine qubit state detection via electron shelving in the 

 D-2(5/2) and F-2(7/2) manifolds in Yb-171(+)},

author = {C. L. Edmunds and T. R. Tan and A. R. Milne and A. Singh and M. J. Biercuk and C. Hempel},

doi = {10.1103/PhysRevA.104.012606},

issn = {2469-9926},

year  = {2021},

date = {2021-07-01},

journal = {PHYSICAL REVIEW A},

volume = {104},

number = {1},

abstract = {Qubits encoded in hyperfine states of trapped ions are ideal for quantum 

 computation given their long lifetimes and low sensitivity to magnetic 

 fields, yet they suffer from off-resonant scattering during detection, 

 often limiting their measurement fidelity. In Yb-171(+) this is 

 exacerbated by a low fluorescence yield, which leads to a need for 

 complex and expensive hardware, a problematic bottleneck especially when 

 scaling up the number of qubits. We demonstrate a detection routine 

 based on electron shelving to address this issue in Yb-171(+) and 

 achieve a 5.6x reduction in single-ion detection error on an avalanche 

 photodiode to 1.8(2) x 10(-3) in a 100 mu s detection period and a 4.3x 

 error reduction on an electron multiplying CCD camera with 7.7(2) x 

 10(-3) error in 400 mu s. We further improve the characterization of a 

 repump transition at 760 nm to enable a more rapid reset of the 

 auxiliary F-2(7/2) states populated after shelving. Finally, we examine 

 the detection fidelity limit using the long-lived F-2(7/2) state, 

 achieving further 300x and 12x reductions in error to 6(7) x 10(-6) and 

 6.3(3) x 10(-4) in 1 ms on the respective detectors. While shelving-rate 

 limited in our setup, we suggest various techniques to realize this 

 detection method at speeds compatible with quantum information 

 processing, providing a pathway to ultrahigh-fidelity detection in 

 Yb-171(+).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000672757000002,

title = {Adaptive filtering of projective quantum measurements using discrete 

 stochastic methods},

author = {Riddhi Swaroop Gupta and Michael J. Biercuk},

doi = {10.1103/PhysRevA.104.012412},

issn = {2469-9926},

year  = {2021},

date = {2021-07-01},

journal = {PHYSICAL REVIEW A},

volume = {104},

number = {1},

abstract = {Adaptive filtering is a powerful class of control theoretic concepts 

 useful in extracting information from noisy data sets or performing 

 forward prediction in time for a dynamic system. The broad utilization 

 of the associated algorithms makes them attractive targets for similar 

 problems in the quantum domain. To date, however, the construction of 

 adaptive filters for quantum systems has typically been carried out in 

 terms of stochastic differential equations for weak, continuous quantum 

 measurements, as used in linear quantum systems such as optical 

 cavities. Discretized measurement models are not as easily treated in 

 this framework, but are frequently employed in quantum information 

 systems leveraging projective measurements. This paper presents a 

 detailed analysis of several technical innovations that enable classical 

 filtering of discrete projective measurements, useful for adaptively 

 learning system dynamics, noise properties, or hardware performance 

 variations in classically correlated measurement data from quantum 

 devices. In previous work we studied a specific case of this framework, 

 in which noise and calibration errors on qubit arrays could be 

 efficiently characterized in space; here, we present a generalized 

 analysis of filtering in quantum systems and demonstrate that the 

 traditional convergence properties of nonlinear classical filtering hold 

 using single-shot projective measurements. These results are important 

 early demonstrations indicating that a range of concepts and techniques 

 from classical nonlinear filtering theory may be applied to the 

 characterization of quantum systems involving discretized projective 

 measurements, paving the way for broader adoption of control theoretic 

 techniques in quantum technology.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000665862400001,

title = {Analog quantum simulation of chemical dynamics},

author = {Ryan J. MacDonell and Claire E. Dickerson and Clare J. T. Birch and Alok Kumar and Claire L. Edmunds and Michael J. Biercuk and Cornelius Hempel and Ivan Kassal},

doi = {10.1039/d1sc02142g},

issn = {2041-6520},

year  = {2021},

date = {2021-07-01},

journal = {CHEMICAL SCIENCE},

volume = {12},

number = {28},

pages = {9794-9805},

abstract = {Ultrafast chemical reactions are difficult to simulate because they 

 involve entangled, many-body wavefunctions whose computational 

 complexity grows rapidly with molecular size. In photochemistry, the 

 breakdown of the Born-Oppenheimer approximation further complicates the 

 problem by entangling nuclear and electronic degrees of freedom. Here, 

 we show that analog quantum simulators can efficiently simulate 

 molecular dynamics using commonly available bosonic modes to represent 

 molecular vibrations. Our approach can be implemented in any device with 

 a qudit controllably coupled to bosonic oscillators and with quantum 

 hardware resources that scale linearly with molecular size, and offers 

 significant resource savings compared to digital quantum simulation 

 algorithms. Advantages of our approach include a time resolution orders 

 of magnitude better than ultrafast spectroscopy, the ability to simulate 

 large molecules with limited hardware using a Suzuki-Trotter expansion, 

 and the ability to implement realistic system-bath interactions with 

 only one additional interaction per mode. Our approach can be 

 implemented with current technology; e.g., the conical intersection in 

 pyrazine can be simulated using a single trapped ion. Therefore, we 

 expect our method will enable classically intractable chemical dynamics 

 simulations in the near term.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bland-Hawthorn2021,

title = {Quantum memories and the double-slit experiment: implications for astronomical interferometry},

author = {Joss Bland-Hawthorn and Matthew J. Sellars and J. G. Bartholomew},

url = {https://www.osapublishing.org/viewmedia.cfm?uri=josab-38-7-A86&seq=0&html=true https://www.osapublishing.org/abstract.cfm?uri=josab-38-7-A86 https://www.osapublishing.org/josab/abstract.cfm?uri=josab-38-7-A86 https://www.osapublishing.org/abstract.cfm?URI},

doi = {10.1364/JOSAB.424651},

issn = {0740-3224},

year  = {2021},

date = {2021-07-01},

journal = {Journal of the Optical Society of America B},

volume = {38},

number = {7},

pages = {A86},

publisher = {The Optical Society},

abstract = {Thomas Young's slit experiment lies at the heart of classical interference and quantum mechanics. Over the last fifty years, it has been shown that particles (e.g. photons, electrons, large molecules), even individual particles, generate an interference pattern at a distant screen after passage through a double slit, thereby demonstrating wave-particle duality. We revisit this famous experiment by replacing both slits with single-mode fibre inputs to two independent quantum memories that are capable of storing the incident electromagnetic field's amplitude and phase as a function of time. At a later time, the action is reversed: the quantum memories are read out in synchrony and the single-mode fibre outputs are allowed to interact consistent with the original observation. In contrast to any classical memory device, the write and read processes of a quantum memory are non-destructive and hence, preserve the photonic quantum states. In principle, with sufficiently long storage times and sufficiently high photonic storage capacity, quantum memories operating at widely separated telescopes can be brought together to achieve optical interferometry over arbitrarily long baselines.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000669051600001,

title = {Quantum Oscillator Noise Spectroscopy via Displaced Cat States},

author = {Alistair R. Milne and Cornelius Hempel and Li Li and Claire L. Edmunds and Harry J. Slatyer and Harrison Ball and Michael R. Hush and Michael J. Biercuk},

doi = {10.1103/PhysRevLett.126.250506},

issn = {0031-9007},

year  = {2021},

date = {2021-06-01},

journal = {PHYSICAL REVIEW LETTERS},

volume = {126},

number = {25},

abstract = {Quantum harmonic oscillators are central to many modem quantum 

 technologies. We introduce a method to determine the frequency noise 

 spectrum of oscillator modes through coupling them to a qubit with 

 continuously driven qubit-state-dependent displacements. We reconstruct 

 the noise spectrum using a series of different drive phase and amplitude 

 modulation patterns in conjunction with a data-fusion routine based on 

 convex optimization. We apply the technique to the identification of 

 intrinsic noise in the motional frequency of a single trapped ion with 

 sensitivity to fluctuations at the sub-Hz level in a spectral range from 

 quasi-dc up to 50 kHz.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{King2021,

title = {Probing strong coupling between a microwave cavity and a spin ensemble with Raman heterodyne spectroscopy},

author = {Gavin G G King and Peter S Barnett and J. G. Bartholomew and Andrei Faraon and Jevon J Longdell},

url = {https://link.aps.org/doi/10.1103/PhysRevB.103.214305},

doi = {10.1103/PhysRevB.103.214305},

issn = {2469-9950},

year  = {2021},

date = {2021-06-01},

journal = {Physical Review B},

volume = {103},

number = {21},

pages = {214305},

abstract = {Raman heterodyne spectroscopy is a powerful tool for characterizing the energy and dynamics of spins. The technique uses an optical pump to transfer coherence from a spin transition to an optical transition where the coherent emission is more easily detected. Here Raman heterodyne spectroscopy is used to probe an isotopically purified ensemble of erbium dopants in a yttrium orthosilicate (Y 2 SiO 5) crystal coupled to a microwave cavity. Because the erbium electron spin transition is strongly coupled to the microwave cavity, we observed Raman heterodyne signals at the resonant frequencies of the hybrid spin-cavity modes (polaritons) rather than the bare erbium spin-transition frequency. Using the coupled system, we made saturation recovery measurements of the ground-state spin relaxation time T 1 = 10 ± 3 s and also observed Raman heterodyne signals using an excited state spin transition. We discuss the implications of these results for efforts toward converting microwave quantum states to optical quantum states.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tu2021,

title = {Tank-Circuit Assisted Coupling Method for Sympathetic Laser Cooling},

author = {Bingsheng Tu and Felix Hahne and Ioanna Arapoglou and Alexander Egl and Fabian Heiße and Martin Höcker and Charlotte König and Jonathan Morgner and Tim Sailer and Andreas Weigel and Robert Wolf and Sven Sturm},

doi = {10.1002/qute.202100029},

year  = {2021},

date = {2021-05-09},

urldate = {2021-05-09},

journal = {Adv. Quantum Technol.},

pages = {2100029},

publisher = {Wiley},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mougeot2021,

title = {Mass measurements of 99–101In challenge ab initio nuclear theory of the nuclide 100Sn},

author = {M. Mougeot and D. Atanasov and J. Karthein and R. N. Wolf and P. Ascher and K. Blaum and K. Chrysalidis and G. Hagen and J. D. Holt and W. J. Huang and G. R. Jansen and I. Kulikov and Yu. A. Litvinov and D. Lunney and V. Manea and T. Miyagi and T. Papenbrock and L. Schweikhard and A. Schwenk and T. Steinsberger and S. R. Stroberg and Z. H. Sun and A. Welker and F. Wienholtz and S. G. Wilkins and K. Zuber},

doi = {10.1038/s41567-021-01326-9},

year  = {2021},

date = {2021-05-01},

journal = {Nat. Phys.},

volume = {17},

pages = {1099},

publisher = {Springer Science and Business Media LLC},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Craiciu2021,

title = {Multifunctional on-chip storage at telecommunication wavelength for quantum networks},

author = {Ioana Craiciu and Mi Lei and Jake Rochman and J. G. Bartholomew and Andrei Faraon},

url = {https://www.osapublishing.org/abstract.cfm?URI=optica-8-1-114},

doi = {10.1364/OPTICA.412211},

issn = {2334-2536},

year  = {2021},

date = {2021-01-01},

journal = {Optica},

volume = {8},

number = {1},

pages = {114},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Xie2021,

title = {Characterization of Er3+:YVO4 for microwave to optical transduction},

author = {Tian Xie and Jake Rochman and J. G. Bartholomew and Andrei Ruskuc and Jonathan M Kindem and Ioana Craiciu and Charles W Thiel and Rufus L Cone and Andrei Faraon},

doi = {10.1103/PhysRevB.104.054111},

issn = {2469-9950},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {Physical Review B},

volume = {104},

number = {5},

pages = {54111},

abstract = {Quantum transduction between microwave and optical frequencies is important for connecting supercon-ducting quantum platforms within a quantum network. Ensembles of rare-earth ions are promising candidates to achieve this conversion due to their collective coherence properties at microwave and optical frequencies. Erbium ions are of particular interest because of their telecom wavelength optical transitions that are compatible with fiber communication networks and components. Here, we report the optical and electron spin properties of erbium-doped yttrium orthovanadate (Er 3+ :YVO 4), including high-resolution optical spectroscopy, electron paramagnetic resonance studies, and an initial demonstration of microwave to optical conversion of classical fields. The highly absorptive optical transitions and narrow ensemble linewidths make Er 3+ :YVO 4 promising for magneto-optic quantum transduction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{bardin2021microwaves,

title = {Microwaves in quantum computing},

author = {Joseph C Bardin and Daniel H Slichter and David J Reilly},

year  = {2021},

date = {2021-01-01},

journal = {IEEE journal of microwaves},

volume = {1},

number = {1},

pages = {403--427},

publisher = {IEEE},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{laucht2021roadmap,

title = {Roadmap on quantum nanotechnologies},

author = {Arne Laucht and Frank Hohls and Niels Ubbelohde and M Fernando Gonzalez-Zalba and David J Reilly and Søren Stobbe and Tim Schröder and Pasquale Scarlino and Jonne V Koski and Andrew Dzurak and others},

year  = {2021},

date = {2021-01-01},

journal = {Nanotechnology},

volume = {32},

number = {16},

pages = {162003},

publisher = {IOP Publishing},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{hasler2021cryogenic,

title = {Cryogenic floating-gate CMOS circuits for quantum control},

author = {Jennifer Hasler and Neil Dick and Kushal Das and Brian Degnan and Alireza Moini and David Reilly},

year  = {2021},

date = {2021-01-01},

journal = {IEEE Transactions on Quantum Engineering},

volume = {2},

pages = {1--10},

publisher = {IEEE},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bartholomew2020,

title = {On-chip coherent microwave-to-optical transduction mediated by ytterbium in YVO4},

author = {J. G. Bartholomew and Jake Rochman and Tian Xie and Jonathan M. Kindem and Andrei Ruskuc and Ioana Craiciu and Mi Lei and Andrei Faraon},

url = {http://www.nature.com/articles/s41467-020-16996-x},

doi = {10.1038/s41467-020-16996-x},

issn = {2041-1723},

year  = {2020},

date = {2020-12-01},

journal = {Nature Communications},

volume = {11},

number = {1},

pages = {3266},

publisher = {Nature Publishing Group},

abstract = {Optical networks that distribute entanglement among various quantum systems will form a powerful framework for quantum science but are yet to interface with leading quantum hardware such as superconducting qubits. Consequently, these systems remain isolated because microwave links at room temperature are noisy and lossy. Building long distance connectivity requires interfaces that map quantum information between microwave and optical fields. While preliminary microwave-to-optical transducers have been realized, developing efficient, low-noise devices that match superconducting qubit frequencies (gigahertz) and bandwidths (10 kilohertz – 1 megahertz) remains a challenge. Here we demonstrate a proof-of-concept on-chip transducer using trivalent ytterbium-171 ions in yttrium orthovanadate coupled to a nanophotonic waveguide and a microwave transmission line. The device′s miniaturization, material, and zero-magnetic-field operation are important advances for rare-earth ion magneto-optical devices. Further integration with high quality factor microwave and optical resonators will enable efficient transduction and create opportunities toward multi-platform quantum networks. Long distance interfaces between superconducting quantum information processing nodes would require coherent, efficient and low-noise microwave-to-optical conversion. Here, the authors use Yb ion ensembles in yttrium orthovanadate to demonstrate a transducer with the potential to fulfill these requirements.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{bardin2020microwaves,

title = {Microwaves in Quantum Computing},

author = {Joseph C Bardin and Daniel H Slichter and David J Reilly},

url = {https://arxiv.org/abs/2011.01480},

year  = {2020},

date = {2020-11-03},

journal = {arXiv preprint arXiv:2011.01480},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{carvalho2020error,

title = {Error-robust quantum logic optimization using a cloud quantum computer interface},

author = {Andre RR Carvalho and Harrison Ball and Michael J Biercuk and Michael R Hush and Felix Thomsen},

url = {https://arxiv.org/abs/2010.08057},

year  = {2020},

date = {2020-10-15},

journal = {arXiv preprint arXiv:2010.08057},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000580591500005,

title = {Integration of spectator qubits into quantum computer architectures for 

 hardware tune-up and calibration},

author = {Riddhi Swaroop Gupta and Luke C. G. Govia and Michael J. Biercuk},

doi = {10.1103/PhysRevA.102.042611},

issn = {2469-9926},

year  = {2020},

date = {2020-10-01},

journal = {PHYSICAL REVIEW A},

volume = {102},

number = {4},

abstract = {Performing efficient quantum computer tune-up and calibration is 

 essential for growth in system complexity. In this work we explore the 

 link between facilitating such capabilities and the underlying 

 architecture of the physical hardware. We focus on the specific 

 challenge of measuring (''mapping'') spatially inhomogeneous 

 quasistatic calibration errors using spectator qubits dedicated to the 

 task of sensing and calibration. We introduce an architectural concept 

 for such spectator qubits: arranging them spatially according to 

 prescriptions from optimal two-dimensional approximation theory. We show 

 that this insight allows for efficient reconstruction of inhomogeneities 

 in qubit calibration, focusing on the specific example of frequency 

 errors which may arise from fabrication variances or ambient magnetic 

 fields. Our results demonstrate that optimal interpolation techniques 

 display near optimal error scaling in cases where the measured 

 characteristic (here the qubit frequency) varies smoothly, and we probe 

 the limits of these benefits as a function of measurement uncertainty. 

 For more complex spatial variations, we demonstrate that the noise 

 mapping for quantum architectures formalism for adaptive measurement and 

 noise filtering outperforms optimal interpolation techniques in 

 isolation and, crucially, can be combined with insights from optimal 

 interpolation theory to produce a general purpose protocol.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pauka2020repairing,

title = {Repairing the surface of InAs-based topological heterostructures},

author = {SJ Pauka and JDS Witt and CN Allen and B Harlech-Jones and A Jouan and GC Gardner and S Gronin and T Wang and C Thomas and MJ Manfra and others},

url = {https://aip.scitation.org/doi/abs/10.1063/5.0014361},

year  = {2020},

date = {2020-09-21},

journal = {Journal of Applied Physics},

volume = {128},

number = {11},

pages = {114301},

publisher = {AIP Publishing LLC},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{WOS:000559297800001,

title = {Simultaneous Spectral Estimation of Dephasing and Amplitude Noise on a 

 Qubit Sensor via Optimally Band-Limited Control},

author = {Virginia Frey and Leigh M. Norris and Lorenza Viola and Michael J. Biercuk},

doi = {10.1103/PhysRevApplied.14.024021},

issn = {2331-7019},

year  = {2020},

date = {2020-08-01},

journal = {PHYSICAL REVIEW APPLIED},

volume = {14},

number = {2},

abstract = {The fragility of quantum systems makes them ideally suited for sensing 

 applications at the nanoscale. However, interpreting the output signal 

 of a qubit-based sensor is generally complicated by background clutter 

 due to out-of-band spectral leakage, as well as ambiguity in signal 

 origin when the sensor is operated with noisy hardware. We present a 

 sensing protocol based on optimally band-limited ``Slepian functions'' 

 that can overcome these challenges, by providing narrowband sensing of 

 ambient dephasing noise, coupling additively to the sensor along the z 

 axis, while permitting isolation of the target noise spectrum from other 

 contributions coupling along a different axis. This is achieved by 

 introducing a finite-difference control modulation, which linearizes the 

 sensor's response and affords tunable band-limited ``windowing'' in 

 frequency. Building on these techniques, we experimentally demonstrate 

 two spectral estimation capabilities using a trapped-ion qubit sensor. 

 We first perform efficient experimental reconstruction of a ``mixed'' 

 dephasing spectrum, composed of a broadband 1/f -type spectrum with 

 discrete spurs. We then demonstrate the simultaneous reconstruction of 

 overlapping dephasing and control noise spectra from a single set of 

 measurements, in a setting where the two noise sources contribute 

 equally to the sensor's response. Our approach provides a direct means 

 to augment quantum-sensor performance in the presence of both complex 

 broadband noise environments and imperfect control signals, by optimally 

 complying with realistic time-bandwidth constraints.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gupta.2020,

title = {Adaptive characterization of spatially inhomogeneous fields and errors in qubit registers},

author = {Riddhi Swaroop Gupta and Claire L Edmunds and Alistair R Milne and Cornelius Hempel and Michael J Biercuk},

doi = {10.1038/s41534-020-0286-0},

year  = {2020},

date = {2020-06-12},

journal = {npj Quantum Information},

volume = {6},

number = {1},

pages = {53},

abstract = {New quantum computing architectures consider integrating qubits as sensors to provide actionable information useful for calibration or decoherence mitigation on neighboring data qubits, but little work has addressed how such schemes may be efficiently implemented in order to maximize information utilization. Techniques from classical estimation and dynamic control, suitably adapted to the strictures of quantum measurement, provide an opportunity to extract augmented hardware performance through automation of low-level characterization and control. In this work, we present an adaptive learning framework, Noise Mapping for Quantum Architectures (NMQA), for scheduling of sensor–qubit measurements and efficient spatial noise mapping (prior to actuation) across device architectures. Via a two-layer particle filter, NMQA receives binary measurements and determines regions within the architecture that share common noise processes; an adaptive controller then schedules future measurements to reduce map uncertainty. Numerical analysis and experiments on an array of trapped ytterbium ions demonstrate that NMQA outperforms brute-force mapping by up to 20× (3×) in simulations (experiments), calculated as a reduction in the number of measurements required to map a spatially inhomogeneous magnetic field with a target error metric. As an early adaptation of robotic control to quantum devices, this work opens up exciting new avenues in quantum computer science.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marciniak2020,

title = {High-power spectral beamsplitter for closely spaced frequencies},

author = {Ch. D Marciniak and A Rischka and R N Wolf and M J Biercuk},

doi = {10.1364/oe.390956},

year  = {2020},

date = {2020-04-01},

journal = {Optics Express},

volume = {28},

number = {8},

pages = {11372},

publisher = {The Optical Society},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kindem2020,

title = {Control and single-shot readout of an ion embedded in a nanophotonic cavity},

author = {Jonathan M. Kindem and Andrei Ruskuc and J. G. Bartholomew and Jake Rochman and Yan Qi Huan and Andrei Faraon},

url = {http://www.nature.com/articles/s41586-020-2160-9},

doi = {10.1038/s41586-020-2160-9},

issn = {0028-0836},

year  = {2020},

date = {2020-04-01},

journal = {Nature},

volume = {580},

number = {7802},

pages = {201--204},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Edmunds.2020,

title = {Dynamically corrected gates suppressing spatiotemporal error correlations as measured by randomized benchmarking},

author = {C L Edmunds and C Hempel and R J Harris and V Frey and T M Stace and M J Biercuk},

doi = {10.1103/physrevresearch.2.013156},

year  = {2020},

date = {2020-01-01},

journal = {Physical Review Research},

volume = {2},

number = {1},

pages = {013156},

abstract = {Quantum error correction provides a path to large-scale quantum computers, but is built on challenging assumptions about the characteristics of the underlying errors. In particular, the mathematical assumption of statistically independent errors in quantum logic operations is at odds with realistic environments where error sources may exhibit strong temporal and spatial correlations. We present experiments using trapped ions to demonstrate that the use of dynamically corrected gates (DCGs), generally considered for the reduction of error magnitudes, can also suppress error correlations in space and time throughout quantum circuits. We present a first-principles analysis of the manifestation of error correlations in randomized benchmarking and validate this model through experiments performed using engineered errors. We find that standard DCGs can reduce error correlations by ∼50× while increasing the magnitude of uncorrelated errors by a factor scaling linearly with the extended DCG duration compared to a primitive gate. We then demonstrate that the correlation characteristics of intrinsic errors in our system are modified by the use of DCGs, consistent with a picture in which DCGs whiten the effective error spectrum induced by external noise.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bentley.2020,

title = {Numeric Optimization for Configurable, Parallel, Error‐Robust Entangling Gates in Large Ion Registers},

author = {Christopher D B Bentley and Harrison Ball and Michael J Biercuk and Andre R R Carvalho and Michael R Hush and Harry J Slatyer},

doi = {10.1002/qute.202000044},

issn = {2511-9044},

year  = {2020},

date = {2020-01-01},

journal = {Advanced Quantum Technologies},

pages = {2000044},

abstract = {A class of entangling gates for trapped atomic ions is studied and the use of numeric optimization techniques to create a wide range of fast, error‐robust gate constructions is demonstrated. A numeric optimization framework is introduced targeting maximally‐ and partially‐entangling operations on ion pairs, multi‐ion registers, multi‐ion subsets of large registers, and parallel operations within a single register. Ions are assumed to be individually addressed, permitting optimization over amplitude‐ and phase‐modulated controls. Calculations and simulations demonstrate that the inclusion of modulation of the difference phase for the bichromatic drive used in the Mølmer–Sørensen gate permits approximately time‐optimal control across a range of gate configurations, and when suitably combined with analytic constraints can also provide robustness against key experimental sources of error. The impact of experimental constraints such as bounds on coupling rates or modulation band‐limits on achievable performance is further demonstrated. Using a custom optimization engine based on TensorFlow, for optimizations on ion registers up to 20 ions, time‐to‐solution of order tens of minutes using a local‐instance laptop is also demonstrated, allowing computational access to system‐scales relevant to near‐term trapped‐ion devices. Numeric optimization and control techniques are demonstrated to create a wide range of fast, robust, high‐fidelity gates. Complex drive controls, with both phase and amplitude modulation on the mediating laser field, are applied to enact multi‐body and parallel operations on chains of up to 20 ions. Control solutions incorporate real constraints on modulation hardware and robustness to laser noise sources.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Milne.2020,

title = {Phase-Modulated Entangling Gates Robust to Static and Time-Varying Errors},

author = {Alistair R Milne and Claire L Edmunds and Cornelius Hempel and Federico Roy and Sandeep Mavadia and Michael J Biercuk},

doi = {10.1103/physrevapplied.13.024022},

year  = {2020},

date = {2020-01-01},

journal = {Physical Review Applied},

volume = {13},

number = {2},

pages = {024022},

abstract = {Entangling operations are among the most important primitive gates employed in quantum computing, and it is crucial to ensure high-fidelity implementations as systems are scaled up. We experimentally realize and characterize a simple scheme to minimize errors in entangling operations related to the residual excitation of mediating bosonic oscillator modes that both improves gate robustness and provides scaling benefits in larger systems. The technique employs discrete phase shifts in the control field driving the gate operation, determined either analytically or numerically, to ensure all modes are de-excited at arbitrary user-defined times. We demonstrate an average gate fidelity of 99.4(2)% across a wide range of parameters in a system of Yb171+ trapped ion qubits, and observe a reduction of gate error in the presence of common experimental error sources. Our approach provides a unified framework to achieve robustness against both static and time-varying laser amplitude and frequency detuning errors. We verify these capabilities through system-identification experiments revealing improvements in error susceptibility achieved in phase-modulated gates.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{ball2020software,

title = {Software tools for quantum control: Improving quantum computer performance through noise and error suppression},

author = {Harrison Ball and Michael J Biercuk and Andre Carvalho and Jiayin Chen and Michael Hush and Leonardo De A Castro and Li Li and Per J Liebermann and Harry J Slatyer and Claire Edmunds and Virginia Frey and Cornelius Hempel and Alistair Milne},

url = {https://arxiv.org/abs/2001.04060},

year  = {2020},

date = {2020-01-01},

journal = {arXiv},

volume = {quant-ph},

number = {2001.04060},

abstract = {Manipulating quantum computing hardware in the presence of imperfect devices and control systems is a central challenge in realizing useful quantum computers. Susceptibility to noise in particular limits the performance and algorithmic capabilities experienced by end users. Fortunately, in both the NISQ era and beyond, quantum control enables the efficient execution of quantum logic operations and quantum algorithms exhibiting robustness to errors, without the need for complex logical encoding. We introduce the first commercial-grade software tools for quantum control in quantum computing research from Q-CTRL, serving the needs of hardware Rtextbackslash&D teams, algorithm developers, and end users. We survey quantum control and its role in combating noise in near-term devices; our primary focus is on quantum firmware, the low-level software solutions designed to enhance the stability of quantum computational hardware at the physical layer. We explain the benefits of quantum firmware not only in error suppression, but also in simplifying compilation protocols and enhancing the efficiency of quantum error correction. We provide an overview of Q-CTRL's software tools for creating and deploying quantum control solutions at various layers of the quantum computing software stack. We describe our software architecture leveraging both distributed cloud computation and local custom integration into hardware systems, and explain how key functionality is integrable with other quantum programming languages. We present a detailed technical overview of product features including a control-optimization engine, filter functions for general systems, and noise characterization. Finally, we present a series of case studies demonstrating the utility of quantum control solutions derived from these tools in improving the performance of trapped-ion and superconducting quantum computer hardware.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tuckett.2020,

title = {Fault-Tolerant Thresholds for the Surface Code in Excess of 5% under Biased Noise},

author = {David K Tuckett and Stephen D Bartlett and Steven T Flammia and Benjamin J Brown},

doi = {10.1103/physrevlett.124.130501},

issn = {0031-9007},

year  = {2020},

date = {2020-01-01},

journal = {Physical Review Letters},

volume = {124},

number = {13},

pages = {130501},

abstract = {Noise in quantum computing is countered with quantum error correction. Achieving optimal performance will require tailoring codes and decoding algorithms to account for features of realistic noise, such as the common situation where the noise is biased towards dephasing. Here we introduce an efficient high-threshold decoder for a noise-tailored surface code based on minimum-weight perfect matching. The decoder exploits the symmetries of its syndrome under the action of biased noise and generalizes to the fault-tolerant regime where measurements are unreliable. Using this decoder, we obtain fault-tolerant thresholds in excess of 6% for a phenomenological noise model in the limit where dephasing dominates. These gains persist even for modest noise biases: we find a threshold of ∼5% in an experimentally relevant regime where dephasing errors occur at a rate 100 times greater than bit-flip errors.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{10.1103/physrevx.10.031041b,

title = {Symmetry-Protected Self-Correcting Quantum Memories},

author = {Sam Roberts and Stephen D Bartlett},

doi = {10.1103/physrevx.10.031041},

year  = {2020},

date = {2020-01-01},

journal = {Physical Review X},

volume = {10},

number = {3},

pages = {031041},

abstract = {A self-correcting quantum memory can store and protect quantum information for a time that increases without bound with the system size and without the need for active error correction. We demonstrate that symmetry can lead to self-correction in 3D spin-lattice models. In particular, we investigate codes given by 2D symmetry-enriched topological (SET) phases that appear naturally on the boundary of 3D symmetry-protected topological (SPT) phases. We find that while conventional on-site symmetries are not sufficient to allow for self-correction in commuting Hamiltonian models of this form, a generalized type of symmetry known as a 1-form symmetry is enough to guarantee self-correction. We illustrate this fact with the 3D “cluster-state” model from the theory of quantum computing. This model is a self-correcting memory, where information is encoded in a 2D SET-ordered phase on the boundary that is protected by the thermally stable SPT ordering of the bulk. We also investigate the gauge color code in this context. Finally, noting that a 1-form symmetry is a very strong constraint, we argue that topologically ordered systems can possess emergent 1-form symmetries, i.e., models where the symmetry appears naturally, without needing to be enforced externally.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{grimsmo2020quantum,

title = {Quantum computing with rotation-symmetric Bosonic codes},

author = {Arne L Grimsmo and Joshua Combes and Ben Q Baragiola},

year  = {2020},

date = {2020-01-01},

journal = {Physical Review X},

volume = {10},

number = {1},

pages = {011058},

publisher = {APS},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{milne2020quantum,

title = {Quantum oscillator noise spectroscopy via displaced Schrödinger cat states},

author = {Alistair R Milne and Cornelius Hempel and Li Li and Claire L Edmunds and Harry J Slatyer and Harrison Ball and Michael R Hush and Michael J Biercuk},

url = {https://arxiv.org/abs/2010.04375},

year  = {2020},

date = {2020-01-01},

journal = {arXiv preprint arXiv:2010.04375},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{smith2020dispersive,

title = {Dispersive readout of Majorana qubits},

author = {Thomas B Smith and Maja C Cassidy and David J Reilly and Stephen D Bartlett and Arne L Grimsmo},

year  = {2020},

date = {2020-01-01},

journal = {PRX Quantum},

volume = {1},

number = {2},

pages = {020313},

publisher = {APS},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{yang2020cryo,

title = {A cryo-CMOS voltage reference in 28-nm FDSOI},

author = {Yuanyuan Yang and Kushal Das and Alireza Moini and David J Reilly},

year  = {2020},

date = {2020-01-01},

journal = {IEEE Solid-State Circuits Letters},

volume = {3},

pages = {186--189},

publisher = {IEEE},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{pauka2020characterizing,

title = {Characterizing quantum devices at scale with custom cryo-CMOS},

author = {SJ Pauka and K Das and JM Hornibrook and GC Gardner and MJ Manfra and MC Cassidy and DJ Reilly},

year  = {2020},

date = {2020-01-01},

journal = {Physical Review Applied},

volume = {13},

number = {5},

pages = {054072},

publisher = {APS},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{jarratt2020detection,

title = {Detection of the Quantum Capacitance of a Point Contact via Dispersive Gate Sensing},

author = {MC Jarratt and SJ Waddy and A Jouan and AC Mahoney and GC Gardner and S Fallahi and MJ Manfra and DJ Reilly},

year  = {2020},

date = {2020-01-01},

journal = {Physical Review Applied},

volume = {14},

number = {6},

pages = {064021},

publisher = {APS},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ball2019,

title = {Site-resolved imaging of beryllium ion crystals in a high-optical-access Penning trap with inbore optomechanics},

author = {H. Ball and Ch. D. Marciniak and R. N. Wolf and A. T. -H. Hung and K. Pyka and M. J. Biercuk},

doi = {10.1063/1.5049506},

year  = {2019},

date = {2019-05-01},

journal = {Rev. Sci. Instrum.},

volume = {90},

number = {5},

pages = {053103},

publisher = {AIP Publishing},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yang.2019,

title = {Silicon qubit fidelities approaching incoherent noise limits via pulse engineering},

author = {C H Yang and K W Chan and R Harper and W Huang and T Evans and J C C Hwang and B Hensen and A Laucht and T Tanttu and F E Hudson and S T Flammia and K M Itoh and A Morello and S D Bartlett and A S Dzurak},

url = {https://www.nature.com/articles/s41928-019-0234-1.epdf?shared_access_token=dwgc0pOWyz17aQfkQBd4wtRgN0jAjWel9jnR3ZoTv0O-UqCO5w04UHpr1iaXzevFLT0JVyPpg9mA3x2230uknqWY4orZ4AuvqFwyDcjiIUIlYS9H_CiaXwr7TrJtnh4_b0MJCLVSEYws_x-aTqCHRw%3D%3D},

doi = {10.1038/s41928-019-0234-1},

year  = {2019},

date = {2019-01-01},

journal = {Nature Electronics},

volume = {2},

number = {4},

pages = {151--158},

abstract = {Spin qubits created from gate-defined silicon metal–oxide–semiconductor quantum dots are a promising architecture for quantum computation. The high single qubit fidelities possible in these systems, combined with quantum error correcting codes, could potentially offer a route to fault-tolerant quantum computing. To achieve fault tolerance, however, gate error rates must be reduced to below a certain threshold and, in general, correlated errors must be removed. Here we show that pulse engineering techniques can be used to reduce the average Clifford gate error rates for silicon quantum dot spin qubits down to 0.043%. This represents a factor of three improvement over state-of-the-art silicon quantum dot devices and extends the randomized benchmarking coherence time to 9.4 ms. By including tomographically complete measurements in our randomized benchmarking, we infer a higher-order feature of the noise called the unitarity, which measures the coherence of noise. This, in turn, allows us to theoretically predict that average gate error rates as low as 0.026% may be achievable with further pulse improvements. These spin qubit fidelities are ultimately limited by incoherent noise, which we attribute to charge noise from the silicon device structure or the environment. Pulse engineering techniques can be used to reduce the average Clifford gate error rates for silicon quantum dot spin qubits down to 0.043%, a factor of three improvement over state-of-the-art silicon devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tuckett.2019,

title = {Tailoring Surface Codes for Highly Biased Noise},

author = {David K Tuckett and Andrew S Darmawan and Christopher T Chubb and Sergey Bravyi and Stephen D Bartlett and Steven T Flammia},

doi = {10.1103/physrevx.9.041031},

year  = {2019},

date = {2019-01-01},

journal = {Physical Review X},

volume = {9},

number = {4},

pages = {041031},

abstract = {The surface code, with a simple modification, exhibits ultrahigh error-correction thresholds when the noise is biased toward dephasing. Here, we identify features of the surface code responsible for these ultrahigh thresholds. We provide strong evidence that the threshold error rate of the surface code tracks the hashing bound exactly for all biases and show how to exploit these features to achieve significant improvement in the logical failure rate. First, we consider the infinite bias limit, meaning pure dephasing. We prove that the error threshold of the modified surface code for pure dephasing noise is 50%, i.e., that all qubits are fully dephased, and this threshold can be achieved by a polynomial time-decoding algorithm. We demonstrate that the subthreshold behavior of the code depends critically on the precise shape and boundary conditions of the code. That is, for rectangular surface codes with standard rough or smooth open boundaries, it is controlled by the parameter g=gcd(j,k), where j and k are dimensions of the surface code lattice. We demonstrate a significant improvement in the logical failure rate with pure dephasing for coprime codes that have g=1 and closely related rotated codes, which have a modified boundary. The effect is dramatic: The same logical failure rate achievable with a square surface code and n physical qubits can be obtained with a coprime or rotated surface code using only O(n) physical qubits. Finally, we use approximate maximum-likelihood decoding to demonstrate that this improvement persists for a general Pauli noise biased toward dephasing. In particular, comparing with a square surface code, we observe a significant improvement in the logical failure rate against biased noise using a rotated surface code with approximately half the number of physical qubits.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}