Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M09: Quantum Error Correction Experiment and Theory (DQI) - Codes and DecodersFocus
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Sponsoring Units: DQI Chair: Alexander Jahn Room: 106 |
Wednesday, March 4, 2020 11:15AM - 11:27AM |
M09.00001: Triangular color codes on trivalent graphs with flag qubits Christopher Chamberland, Aleksander Kubica, Theodore Yoder, Guanyu Zhu The color code is a topological quantum error-correcting code with a variety of computationally-valuable and fault-tolerant logical gates. Its two-dimensional version, the triangular color code, may soon be realized with currently available superconducting hardware limited by qubit connectivity. To guide the experimental effort, we thus study the storage threshold of the triangular color code against the circuit-level depolarizing noise. First, we adapt the Restriction Decoder to the setting of the triangular color code and to phenomenological noise. Then, we propose a fault-tolerant implementation of the stabilizer measurement circuits, which incorporates flag qubits. We show how information from flag qubits can be use with the Restriction Decoder to maintain the effective distance of the code. We numerically estimate the threshold of the triangular color code to be 0.2%, which is competitive with the thresholds of other topological quantum codes. Lastly, we prove that using 1-flag stabilizer measurement circuits are enough to recover the full distance of the code. |
Wednesday, March 4, 2020 11:27AM - 11:39AM |
M09.00002: A numerical error threshold for "colorful" quantum computing Josey Hanish, Skylar Turner, Eoin Blanchard, Noah Davis, Brian La Cour "Colorful" quantum computing was first proposed by Héctor Bombín to realize universal, fault-tolerant quantum computing using 3D color codes, or tetrahedral codes. Unlike the well-studied surface code methods, colorful quantum computing does not require magic state distillation and instead relies on a universal set of transversal gates and measurements. Colorful quantum computing can be realized in either a 3D or a 2D system. In this paper, we numerically test 3D colorful quantum computing's resilience to noise. In addition to the independent and identically distributed noise that affects the initial state, we must also correct errors that arise as part of the initialization process. We find a threshold for fault-tolerance on the body-centered cubic lattice. This threshold upper-bounds the more experimentally feasible 2D colorful quantum computing scheme and hopefully motivates research into color code methods of quantum computing. |
Wednesday, March 4, 2020 11:39AM - 11:51AM |
M09.00003: Reinforcement learning for toric code error correction Mats Granath, Mattias Eliasson, David Fitzek, Anton Frisk Kockum I will present a summary of our efforts to use deep reinforcement learning (DRL) for quantum error correction of the toric code. A convolutional neural network is trained by exploration of the state space consisting of (hidden) error configurations and corresponding (visible) syndromes. No external input to the algorithm is provided apart from the current syndrome and the final success or failure of the correction episode. The trained network outputs action values of Pauli operations on the system given an input syndrome. Initial work on uncorrelated noise has shown that the DRL agent performs on par with the standard minimum weight perfect matching (MWPM) algorithm1. For depolarizing noise the algorithm outperforms MWPM for all error probabilities and with a higher error threshold. The progress on extending this framework to deal with arbitrarily biased noise and syndrome measurement errors, as well as the scalability of the approach will be discussed. |
Wednesday, March 4, 2020 11:51AM - 12:27PM |
M09.00004: Qubit surface codes from rotation systems acting on Majorana fermions Invited Speaker: Theodore Yoder A rotation system is a combinatorial description of a graph and its embedding in a 2-dimensional manifold defined by two permutations on a set of objects. We instantiate this set of objects with Majorana operators and define a Majorana code by associating stabilizers to vertices and faces of the graph embedding. We show how the resulting Majorana code corresponds to a qubit stabilizer code that generalizes the known constructions of rotated and twisted surface codes. While we obtain similar macroscopic behavior -- for instance, anyon type changing when crossing defect lines -- the microscopic details of our codes can lead to improved code parameters. For instance, we identify the [[5,1,3]] code as the smallest member of a surface code family on the torus. We find other code families (both in the plane and on higher genus surfaces) improving upon the constants in the Bravyi-Poulin-Terhal bound. |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M09.00005: Considerations for incorporating small logical qubits in digital error correction codes David Rodriguez Perez, Eliot Kapit We introduce a hybrid error correction scheme by considering using traditional error correcting codes (e.g. Surface codes) with small logical qubit architectures, namely, the Very Small Logical Qubit (VSLQ). Previous theoretical work has shown that the VSLQ can achieve a linear scaling improvement factor, with a single qubit T1 lifetime of 30 µs having a logical lifetime of up to 3 ms, all while using two high-coherence qubits and two lossy qubits or resonators, using passive error correction. In this talk, we consider using small logical qubits such as the VSLQ as part of a broader measurement-based code, and explore potential advantages and challenges from such a hybrid approach. In particular, given that digital error correction normally does not account for qubit leakage error, we explore the complexity that would be introduced in dealing with the corresponding leakage error from VSLQ logical states, as well as other concerns. |
Wednesday, March 4, 2020 12:39PM - 12:51PM |
M09.00006: Higher-order autonomous quantum error correction Jose Lebreuilly, Kyungjoo Noh, Chiao-Hsuan Wang, Steven Girvin, Liang Jiang Autonomous quantum error correction (AutoQEC) harnesses engineered coupling to an external reservoir to protect quantum information from decoherence. First-order codes provide protection against a single fault and have simple structures. However, as a counterpart they suffer from the drawback of requiring an engineered dissipation that is typically orders of magnitude stronger than natural dissipation. In this work, we investigate the higher-order case and identify Knill-Laflamme conditions which, if satisfied up to some order r, lead to the existence of an AutoQEC protocol providing protection against at most r consecutive errors. Furthermore, we develop a general theoretical framework for analyzing the effective dynamics in the protected code space. Within this framework we show that the effective decay rate decreases exponentially in r, exceeding the first-order code performance already for moderate engineered dissipation strengths. Finally, we demonstrate that the AutoQEC scheme can be combined with an error-transparent Hamiltonian so as to perform a unitary quantum computation over time scales which far exceed the physical qubits lifetime. |
Wednesday, March 4, 2020 12:51PM - 1:03PM |
M09.00007: Characterization and critical faults of leakage errors on the surface code Natalie Brown, Andrew Cross, Kenneth Brown Leakage is a particularly damaging error that occurs when a qubit leaves the defined computational subspace. Leakage errors leave qubits ill-defined and limit the effectiveness of quantum error correcting codes. The effects of leakage errors on the surface code has been studied in various contexts. However, the effects of a leaked data qubit versus a leaked ancilla qubit can be quite different. |
Wednesday, March 4, 2020 1:03PM - 1:15PM |
M09.00008: Fault tolerance on near-term trapped-ion logical qubits with a neural-network decoder David Obando Vargas, Yefry Lopez, Mauricio Gutierrez A crucial step towards the construction of a fault-tolerant quantum computer is the implementation of a logical qubit with a higher fidelity than its constituent physical qubits. In this context, we perform simulations of three promising distance-3 quantum error-correcting codes: the color, surface, and Bacon-Shor codes implemented on a state-of-the-art ion trap with realistic noise sources. Our goal is to find the break-even point where the logical memory outperforms the physical one. In previous works [1], after each error correction step, a correction was performed based exclusively on the syndromes of that step. We now use the syndromes of all previous error correction steps and employ a neural-network-based decoder, which has the advantage of not discarding the syndrome history and also being flexible to different noise models. For each code, we compare the two correction approaches and find a clear improvement in the logical fidelity when the neural-network-based decoder is used. These results will serve as a useful guide to future experiments. |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M09.00009: Implementing a Logical Qubit on a Trapped Ion Quantum Information Processor Laird Egan, Marko Cetina, Michael L Goldman, Andrew Risinger, Crystal Noel, Daiwei Zhu, Debopriyo Biswas, Christopher Roy Monroe Under the IARPA Logical Qubit (LogiQ) program, we aim to demonstrate a logical qubit using the Bacon-Shor [[9,1,3]] subsystem code. Towards this goal, we built a universal ion-trap quantum processor capable of individual qubit addressing, sympathetic cooling, and ancilla readout. The Bacon-Shor code consists of 9 data qubits, encoding 1 logical qubit, with stabilizer circuits mapped to 4 ancilla qubits capable of correcting any single qubit error. In this talk, we report on the experimental progress made towards implementation of quantum error correction, including the encoding of the logical qubit and stabilizer readout. Additionally, we will lay out the near-term path for achieving multiple rounds of error correction and the prospects for surpassing the quantum error threshold. |
Wednesday, March 4, 2020 1:27PM - 1:39PM |
M09.00010: Environment noise analysis and real-time decoupling feedback control for a Nitrogen-Vacancy center Arshag Danageozian, Nathaniel Miller, Pratik Barge, Narayan Bhusal, Jonathan P Dowling Nitrogen-Vacancy (NV) centers in diamond have shown to be a very promising candidate for applications of quantum information processing. Given that a small percentage of the Carbon atoms in diamond are Carbon 13 isotopes, we consider how the collective nuclear spins of these atoms affect the nuclear spin state of the Nitrogen 15 atom of the NV center, which is used as our computational qubit. We accomplish this by isolating a three level lambda system out of the electronic structure of the NV center and observing the phenomenon of coherent population trapping. The information gained from this observation is used to find the optimum dynamical decoupling pulse sequence that will help us preserve the state of our computational qubit for a set duration of time. |
Wednesday, March 4, 2020 1:39PM - 1:51PM |
M09.00011: Mediator assisted cooling in quantum annealing Manuel Pino Garcia, Juan José García-Ripoll We show a significant reduction of errors for an architecture of quantum annealing where bosonic modes mediate the interaction between qubits. These systems have a large redundancy in the subspace of solutions, as there are solutions with arbitrarily bosonic occupancies. We explain how this redundancy leads to a mitigation of errors when the bosonic modes work in the ultra-strong coupling regime. Our numerical simulations predict a large increase of qubits coherence for an specific annealing problem with mediated interactions. We provide evidences that error reduction could also occurs in other types of quantum computers with similar architectures. |
Wednesday, March 4, 2020 1:51PM - 2:03PM |
M09.00012: Combined continuous error suppression and error correction for quantum annealing Juan Atalaya, Birgitta K Whaley, Murphy Yuezhen Niu The scheme of Jordan, Farhi and Shor for error suppression during quantum annealing [Phys. Rev. A 74, 052322 (2006)] adds energy penalty terms to an encoded Hamiltonian. The role of these penalty terms is to suppress the occurrence of errors taking the encoded quantum state out of the code space. However, errors can still occur in this scheme, albeit with lowered probability. Here we address the question of whether continuous error correction can enhance the performance of quantum annealing by further correcting the remaining unsuppressed errors. To answer this question we consider the continuous implementation of the three-qubit bit-flip quantum error correcting code, where the error syndrome operators are continuously and simultaneously measured. We show that, under certain conditions, continuous error correction combined with error suppression can lead to significantly improved final ground state fidelities. A notable feature of the combined protocol is that it requires quantum error correction operations which are different from those typically used in the operation of quantum memory under this encoding. We also discuss generalization of these results to other quantum error correcting codes. |
Wednesday, March 4, 2020 2:03PM - 2:15PM |
M09.00013: Continuous error correction for evolution under time-dependent Hamiltonians Song Zhang, Juan Atalaya, Murphy Yuezhen Niu, Arman Babakhani, Jeffrey Epstein, Herman Chan, Birgitta K Whaley
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