01807nas a2200181 4500008004100000022001400041245003600055210003500091260001400126490000600140520134200146100001501488700002301503700001701526700002401543700002101567856003701588 2024 eng d a2691-339900aClifford-Deformed Surface Codes0 aCliffordDeformed Surface Codes c3/19/20240 v53 a

Various realizations of Kitaev's surface code perform surprisingly well for biased Pauli noise. Attracted by these potential gains, we study the performance of Clifford-deformed surface codes (CDSCs) obtained from the surface code by applying single-qubit Clifford operators. We first analyze CDSCs on the 3×3 square lattice and find that, depending on the noise bias, their logical error rates can differ by orders of magnitude. To explain the observed behavior, we introduce the effective distance d′, which reduces to the standard distance for unbiased noise. To study CDSC performance in the thermodynamic limit, we focus on random CDSCs. Using the statistical mechanical mapping for quantum codes, we uncover a phase diagram that describes random CDSC families with 50% threshold at infinite bias. In the high-threshold region, we further demonstrate that typical code realizations outperform the thresholds and subthreshold logical error rates, at finite bias, of the best-known translationally invariant codes. We demonstrate the practical relevance of these random CDSC families by constructing a translation-invariant CDSC belonging to a high-performance random CDSC family. We also show that our translation-invariant CDSC outperforms well-known translation-invariant CDSCs such as the XZZX and XY codes.

1 aDua, Arpit1 aKubica, Aleksander1 aJiang, Liang1 aFlammia, Steven, T.1 aGullans, Michael uhttps://arxiv.org/abs/2201.0780201587nas a2200181 4500008004100000245010600041210006900147260001400216520099600230653002701226653003101253100001801284700001701302700001501319700001701334700001701351856003701368 2022 eng d00aShadow Distillation: Quantum Error Mitigation with Classical Shadows for Near-Term Quantum Processors0 aShadow Distillation Quantum Error Mitigation with Classical Shad c3/14/20223 a

Mitigating errors in quantum information processing devices is especially important in the absence of fault tolerance. An effective method in suppressing state-preparation errors is using multiple copies to distill the ideal component from a noisy quantum state. Here, we use classical shadows and randomized measurements to circumvent the need for coherent access to multiple copies at an exponential cost. We study the scaling of resources using numerical simulations and find that the overhead is still favorable compared to full state tomography. We optimize measurement resources under realistic experimental constraints and apply our method to an experiment preparing Greenberger-Horne-Zeilinger (GHZ) state with trapped ions. In addition to improving stabilizer measurements, the analysis of the improved results reveals the nature of errors affecting the experiment. Hence, our results provide a directly applicable method for mitigating errors in near-term quantum computers.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aSeif, Alireza1 aCian, Ze-Pei1 aZhou, Sisi1 aChen, Senrui1 aJiang, Liang uhttps://arxiv.org/abs/2203.0730901645nas a2200205 4500008004100000245008200041210006900123260001500192300001100207490000700218520102200225100001501247700002401262700002101286700001701307700001601324700002701340700001701367856005501384 2016 eng d00aOptimized tomography of continuous variable systems using excitation counting0 aOptimized tomography of continuous variable systems using excita c2016/11/21 a0523270 v943 a

We propose a systematic procedure to optimize quantum state tomography protocols for continuous variable systems based on excitation counting preceded by a displacement operation. Compared with conventional tomography based on Husimi or Wigner function measurement, the excitation counting approach can significantly reduce the number of measurement settings. We investigate both informational completeness and robustness, and provide a bound of reconstruction error involving the condition number of the sensing map. We also identify the measurement settings that optimize this error bound, and demonstrate that the improved reconstruction robustness can lead to an order-of-magnitude reduction of estimation error with given resources. This optimization procedure is general and can incorporate prior information of the unknown state to further simplify the protocol.

1 aShen, Chao1 aHeeres, Reinier, W.1 aReinhold, Philip1 aJiang, Luyao1 aLiu, Yi-Kai1 aSchoelkopf, Robert, J.1 aJiang, Liang uhttp://link.aps.org/doi/10.1103/PhysRevA.94.05232701465nas a2200205 4500008004100000245006900041210006800110260001500178300001100193490000700204520085500211100002201066700001401088700001901102700002001121700002101141700001701162700002501179856005501204 2016 eng d00aSubwavelength-width optical tunnel junctions for ultracold atoms0 aSubwavelengthwidth optical tunnel junctions for ultracold atoms c2016/12/27 a0634220 v943 a

We propose a method for creating far-field optical barrier potentials for ultracold atoms with widths that are narrower than the diffraction limit and can approach tens of nanometers. The reduced widths stem from the nonlinear atomic response to control fields that create spatially varying dark resonances. The subwavelength barrier is the result of the geometric scalar potential experienced by an atom prepared in such a spatially varying dark state. The performance of this technique, as well as its applications to the study of many-body physics and to the implementation of quantum-information protocols with ultracold atoms, are discussed, with a focus on the implementation of tunnel junctions.

1 aJendrzejewski, F.1 aEckel, S.1 aTiecke, T., G.1 aJuzeliƫnas, G.1 aCampbell, G., K.1 aJiang, Liang1 aGorshkov, Alexey, V. uhttp://link.aps.org/doi/10.1103/PhysRevA.94.063422