Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R51: Error CorrectionFocus
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Sponsoring Units: GQI Chair: Mark Byrd, University of Southern California Room: 398 |
Thursday, March 16, 2017 8:00AM - 8:36AM |
R51.00001: Passive Error Correction and Gates for a Very Small Logical Qubit Invited Speaker: Eliot Kapit In this talk, I discuss further theoretical developments of the proposed "Very Small Logical Qubit" architecture, which promises order-of-magnitude coherence increases over any of its component parts for T1 and T2 values commonly achieved in experiments. These improvements come from engineered dissipation and do not require active measurement or intervention. However, to be useful for constructing a quantum computer, gate error must be reduced as well. To do so, I propose a realistic implementation of a universal one- and two-qubit gate set for the VSLQ, with finely tuned gate operations that are resilient to random errors which occur mid-gate. I numerically benchmark the operations to demonstrate improved gate fidelity, with superlinear reduction in gate error with linear increase in T1. These results suggest that small logical qubits could be integrated into a measurement-based code for improved error correction performance. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R51.00002: Architectural analysis of universal concatenated quantum codes Tomas Jochym-O'Connor, Christopher Chamberland, Raymond Laflamme Concatenated quantum error correction provides a means towards fault-tolerant quantum computation. Moreover, a set of universal gates can be implemented through the concatenation of different error correcting codes, eliminating the need for magic state distillation. This work addresses the architectural costs of such an implementation and compares it to the leading candidate in the field, the surface code. We use a hybrid decoding scheme with a form of message passing between pairs of complementary codes and hard decoding between higher concatenation levels. While providing a favourable asymptotic threshold when compared to other concatenated schemes in the gate error model, we show that the concatenated code construction with the studied decoding algorithm will have high overhead costs when compared to the surface code construction assisted by distillation. We attribute this difference in overhead costs as a result of the difference in fault-tolerance threshold rates between the codes. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R51.00003: Finite temperature protocols for stabilizer codes with few measurements C. Daniel Freeman, Mohan Sarovar, Chris Herdman, Birgitta Whaley We present an analysis of a new class of algorithms for finite temperature stabilizer error correction codes with stringlike errors. In particular, we treat algorithms that only require measurements of a subset of stabilizer operators, and we elaborate on how this restriction affects the thresholds of known stabilizer codes like the toric code. Using a mixture of continuous-time Monte Carlo and quantum master equation methods, we provide explicit calculations of the nonequilibrium dynamics for these codes, as well as temperature-dependent error correction thresholds. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R51.00004: A three-qubit superconducting circuit implementing pairwise longitudinal coupling Tanay Roy, Suman Kundu, Madhavi Chand, Sumeru Hazra, N. Nehra, R. Cosmic, A. Ranadive, Meghan P. Patankar, Kedar Damle, R. Vijay We present a superconducting circuit, the ``trimon'', consisting of three qubits in the 3D circuit-QED architecture with pairwise longitudinal coupling. The design is based on the Josephson Ring Modulator where the three orthogonal anharmonic oscillator modes act as three transmon-type qubits. The strong inter-qubit longitudinal coupling is always-on and enables fast controlled rotations delivering a universal set of gates. We will describe our joint readout technique for single-shot measurement of the trimon device. We will then present our implementation of single-pulse high-fidelity CNOT gate and optimal SWAP operation between pairs of qubits. We will conclude by discussing the extension to three-qubit gates like Toffoli and Fredkin and present preliminary results. Reference: arXiv:1610.07915. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R51.00005: Bit-flip error correction in a novel three-qubit superconducting circuit Suman Kundu, Tanay Roy, Sumeru Hazra, Madhavi Chand, A. Ranadive, Meghan P. Patankar, R. Vijay We propose implementation of three-qubit bit-flip error correction protocol based on parity measurement using a novel three-qubit system called the ``trimon''. The pairwise longitudinal coupling between the three qubits enables simple encoding and decoding of the bit-flip error code. Further, the trimon device enables joint readout of the three-qubit state using standard dispersive readout in the 3D circuit-QED architecture. I will describe our dispersive readout technique and the procedure for implementing parity measurements without using ancilla-qubits. I will conclude by presenting some preliminary results and possibility of extending such techniques for other error-correcting codes. Reference: arXiv:1610.07915. [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R51.00006: Continuously monitoring the parity of superconducting qubits in a 2D cQED architecture Machiel Blok, Emmanuel Flurin, William Livingston, James Colless, Allison Dove, Irfan Siddiqi Continuous measurements of joint qubit properties such as their parity can reveal insight into the collapse dynamics of entangled states and are a prerequisite for implementing continuous quantum error correction. Here it is crucial that the measurement collects no information other than the parity to avoid measurement induced dephasing. In a cQED architecture, a full-parity measurement can be implemented by strongly coupling two transmon qubits to a single high-Q planar resonator ($\chi \gg \kappa$). We will discuss the experimental implementation of this on-chip technique and the prospects to extend it to more qubits. This will allow us to monitor, in real-time, the projection into multi-partite entangled states and continuously detect errors on a logical qubit encoded in an entangled subspace. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R51.00007: Abstract Withdrawn
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Thursday, March 16, 2017 9:48AM - 10:00AM |
R51.00008: Effect of deterministic errors on quantum error protection circuitry Yunseong Nam, Reinhold Bl\"umel Quantum error protection circuitry is not always useful. A balance has to be struck between its usefulness for correcting errors and its downside as a source for generating errors. In the real world, quantum error protection circuitry consists of physical gates, which are not perfect in principle. Therefore, it is important to investigate whether due to the unavoidable flaws in its quantum gates, error correction circuitry does more harm than good. What is the role of the Threshold Theorem in this? This talk is going to discuss this question and in addition present systems, such as decomposition sequences, in which the tug-of-war between the beneficial aspects of the quantum error correction circuitry and the downside of the hardware errors is illustrated. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R51.00009: Logical error rates and resource overheads of non-transversal, magic-less gates Ryuji Takagi, Theodore J. Yoder, Isaac L. Chuang A non-transversal gate is required for a quantum error correcting code to perform universal computation. Gate teleportation using magic states is one way to perform the necessary operation, albeit with large overhead. Several constructions of logical gates have been proposed without magic states, but little work has been done to evaluate logical error rates and resource overheads of the gates, and compare them to magic states. In this work, we calculate logical error rates of controlled-controlled-$Z$ (CCZ) gates on 5-qubit code and 7-qubit code implemented with the recently proposed pieceably fault-tolerant construction, which uses neither magic states nor additional ancilla qubits other than those used for error correction. Alongside transversal gates on these codes, CCZ is enough for universal computation. We also calculate the error rate of performing CCZ by state injection. Despite being much more costly in terms of space and time, state injection is no less error-prone than pieceable constructions. Our result also serves as motivation to investigate different choices of universal gate sets other than the conventional one, Clifford gates + $T$ gate. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R51.00010: Optimization of passive error correction parameters for the Very Small Logical Qubit David Rodriguez Perez, Eric Holland, Jonathan Dubois, Eliot Kapit The Very Small Logical Qubit is a promising route to passive error correction in superconducting qubit architectures. However; optimal circuit parameters for given single qubit lifetimes and nonlinearities are not yet known. We describe a numerical optimization scheme to find the optimal device and signal parameters to maximize the logical state lifetime in simulations with realistic single qubit error rates, and report theoretical coherence times T$_{L}$ exceeding 1 ms for single qubit T$_{1}$ as low as 20 $\mu $s. These results clearly illustrate the tradeoff between rapid error correction and noise induced by the error correction mechanism itself. Further, we consider higher order corrections beyond the three-level approximation, and show that their effects can be easily mitigated. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R51.00011: Continuous-variable quantum error correction I: code comparison Victor V. Albert, Kasper Duivenvoorden, Kyungjoo Noh, R. T. Brierley, Philip Reinhold, Linshu Li, Chao Shen, R. J. Schoelkopf, S. M. Girvin, Barbara M. Terhal, Liang Jiang There are currently four types of non-trivial encodings of quantum information in a single bosonic mode: cat, binomial, and numerically optimized codes are designed to protect against bosonic loss errors, while GKP codes are designed to protect against bosonic displacement errors. These four code types have yet to be compared using the same error model. We report on a numerical comparison of the entanglement fidelity of all codes with respect to the lossy bosonic channel, given an average occupation number constraint and the optimal recovery operation. GKP codes demonstrate the highest fidelities for all but the smallest values of the boson loss probability (the parameter which quantifies the strength of amplitude damping). Although designed to protect against small displacement noise, GKP codes can offer a high degree of protection against bosonic loss errors. We also examine the performance of the four code types with respect to the combination of amplitude damping and a strong Kerr non-linearity. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R51.00012: Continuous-variable quantum error correction II: the Gottesman-Kitaev-Preskill code Kyungjoo Noh, Kasper Duivenvoorden, Victor V. Albert, R. T. Brierley, Philip Reinhold, Linshu Li, Chao Shen, R. J. Schoelkopf, S. M. Girvin, Barbara M. Terhal, Liang Jiang Recently, various single mode bosonic quantum error-correcting codes (e.g., cat codes and binomial codes) have been developed to correct errors due to excitation loss of bosonic systems. Meanwhile, the Gottesman-Kitaev-Preskill (GKP) codes do not follow the simple design guidelines of cat and binomial codes, but nevertheless demonstrate excellent performance in correcting bosonic loss errors. To understand the underlying mechanism of the GKP codes, we represent them using a superposition of coherent states, investigate their performance as approximate error-correcting codes, and identify the dominant types of uncorrectable errors. This understanding will help us to develop more robust codes against bosonic loss errors, which will be useful for robust quantum information processing with bosonic systems. [Preview Abstract] |
Thursday, March 16, 2017 10:48AM - 11:00AM |
R51.00013: Quantum error correction in classical analog devices Brian La Cour, Corey Ostrove, Sean Lanham, Granville Ott Quantum computers are believed to be fundamentally different from classical analog devices due to the possibility that the former may be operated in a fault-tolerant manner. According to the threshold theorem, quantum error correction may be used to improve the fidelity of a logical gate operation over those of the constituent physical gate operations, provided that the latter are of sufficient fidelity. In this talk we will describe an experimental demonstration of a classical analog device capable of emulating a universal gate-based quantum computer using a wavetrain of analog signals to represent a multi-qubit state. By programming the device to execute a simple quantum error correction protocol, we are able to demonstrate an improvement in the overall gate fidelity. [Preview Abstract] |
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