Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X15: Quantum Error Correction and Fault-Tolerance |
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Sponsoring Units: DQI Chair: Stephen Jordan, NIST -Natl Inst of Stds & Tech Room: LACC 304C |
Friday, March 9, 2018 8:00AM - 8:12AM |
X15.00001: Generation and Decoding of Random Sparse Stabilizer Codes Stefan Krastanov, Liang Jiang Over the last few years there has been increasing interest in the design of sparse quantum error correcting codes, inspired by the great success of their classical counterpart, the low density parity check codes (LDPCs). However, two difficulties arise in this pursuit: it has proven difficult to extend the CSS formalism to the creation of quantum LDPC codes with non-vanishing rates; moreover, efficiently decoding quantum LDPC codes is unsolved problem as the iterative belief propagation decoders used for classical codes do not converge when applied to quantum codes. We explore machine learning techniques for decoding as well as generating efficient codes from this class. |
Friday, March 9, 2018 8:12AM - 8:24AM |
X15.00002: Multi-path Summation for Decoding 2D Topological Codes Daniel Criger, Imran Ashraf Fault tolerance is a prerequisite for scalable quantum computing. |
Friday, March 9, 2018 8:24AM - 8:36AM |
X15.00003: Efficient and Fault-Tolerant Preparation of Large Block Code Ancilla States Todd Brun, Ching-Yi Lai, Yi-Cong Zheng Fault-tolerant quantum computation (FTQC) schemes that use multi-qubit large block codes can potentially reduce the resource overhead to a great extent. A major obstacle is the requirement of a large number of of clean ancilla states of different types without correlated errors inside each block. These ancilla states are usually logical stabilizer states of the data code blocks, which are generally difficult to prepare if the code size is large. Previously we have proposed an ancilla distillation protocol for Calderbank-Shor-Steane (CSS) codes by classical error-correcting codes. It was assumed that the quantum gates in the distillation circuit were perfect; however, in reality noisy quantum gates may introduce correlated errors that are not treatable by the protocol. In arXiv:1710.00389 we show that additional postselection by another classical error-detecting code can be applied to remove almost all correlated errors. Consequently, the revised protocol is fully fault-tolerant and capable of preparing a large set of stabilizer states sufficient for FTQC using large block codes. At the same time, the yield rate can be high for general CSS codes of arbitrary size. |
Friday, March 9, 2018 8:36AM - 8:48AM |
X15.00004: Fault-tolerant quantum computation with non-deterministic entangling gates Mercedes Gimeno-Segovia, James Auger, Hussain Anwar, Thomas Stace, Dan Browne Performing entangling gates between physical qubits is necessary for building a large-scale univer- sal quantum computer, but in some physical implementations—for example, those that are based on linear optics or networks of ion traps—entangling gates can only be implemented probabilistically. In this work, we study the fault-tolerant performance of a topological cluster state scheme with local non-deterministic entanglement generation, where failed entangling gates (which correspond to bonds on the lattice representation of the cluster state) lead to a defective three-dimensional lattice with missing bonds. We present two approaches for dealing with missing bonds; the first is a non-adaptive scheme that requires no additional quantum processing, and the second is an adaptive scheme in which qubits can be measured in an alternative basis to effectively remove them from the lattice, hence eliminating their damaging effect and leading to better threshold performance. We find that a fault-tolerance threshold can still be observed with a bond-loss rate of 6.5% for the non-adaptive scheme, and a bond-loss rate as high as 14.5% for the adaptive scheme. |
Friday, March 9, 2018 8:48AM - 9:00AM |
X15.00005: Multi-photon experiments with solid-state single-photon sources Marcelo De Almeida, Nor Azwa Zakaria, Jihun Cha, Raphael Abrahao, Andrew White Solid-state emitters, such as semiconductor quantum dots, are a promising platform for single-photon sources. Recent breakthroughs in material syntheses and fabrication enabled a new generation of devices, combining high emission brightness with a near unity indistinguishable pure single-photon output. |
Friday, March 9, 2018 9:00AM - 9:12AM |
X15.00006: Comparing Zeeman qubits to hyperfine qubits in the context of the surface code: ^{171}Yb^{+} and ^{174}Yb^{+} Natalie Brown, Ken Brown Many systems used for quantum computing possess additional states beyond those defining the qubit. Leakage out of the qubit subspace must be considered when designing quantum error correction codes (QECC). Here we consider trapped ion qubits manipulated by Raman transitions. Zeeman qubits do not suffer from leakage errors but are sensitive to magnetic fields to first-order. Hyperfine qubits can be encoded in clock states that are insensitive to magnetic fields to first-order, but spontaneous scattering during the Raman transition can lead to leakage. Here we compare a Zeeman qubit (^{174}Yb^{+}) to a hyperfine qubit (^{171}Yb^{+}) in the context of the surface code. We find that the number of physical qubits required to reach a specific logical qubit error can be reduced by using ^{174}Yb^{+} if the magnetic field can be stabilized to 10 μG. |
Friday, March 9, 2018 9:12AM - 9:24AM |
X15.00007: Robust Non-Clifford gate for Parafermions Arpit Dua, Bors Malomed, Meng Cheng, Liang Jiang Anyon models of Parafermions can be extended through the addition of a quantized fractional flux and made universal. Braiding of Parafermions provides the Clifford gates while the braiding of a quantized fractional flux around a pair of Parafermions can provide the requisite Non-Clifford gate needed for universality of quantum gates. For example, braiding of half fluxon with h/4e quantized flux around Z_N(N>2) parafermion pair can provide the Non-Clifford Z^(1/2) gate, where Z is the logical qudit operator. Josephson junction made of spin-triplet superconductors can host a half fluxon which can be braided around parafermionic defects implementing the Z^(1/2) gate. We demonstrate the implementation of this Non-Clifford gate and investigate its robustness. |
Friday, March 9, 2018 9:24AM - 9:36AM |
X15.00008: Quantum Origami: Applying Fault-tolerant Transversal Gates and Measuring Topological Order Guanyu Zhu, Mohammad Hafezi, Maissam Barkeshli In topology, a torus remains invariant under certain non-trivial transformations known as modular transformations. In the context of topologically ordered quantum states of matter, these transformations encode the braiding statistics and fusion rules of emergent anyonic excitations and thus serve as a diagnostic of topological order. Moreover, modular transformations of higher genus surfaces, e.g., a torus with multiple handles, can enhance the computational power of a topological state, in many cases providing a universal fault-tolerant set of gates for quantum computation. However, due to the intrusive nature of modular transformations, which abstractly involve global operations and manifold surgery, physical implementations of them in local systems have remained elusive. Here, we show that by folding manifolds and introducing twist defects, modular transformations can be reduced to independent local unitaries, specifically, a finite sequence of local SWAP gates between the layers, providing a novel class of transversal logic gates in topological codes and leading to universal gate set. We further propose methods to directly measure the modular matrices, and thus the fractional statistics of anyonic excitations, providing a novel way to directly measure topological order. |
Friday, March 9, 2018 9:36AM - 9:48AM |
X15.00009: Efficient Error Corrected Quantum Teleportation Matthew Otten, Stephen Gray In near term quantum computers, each qubit will be a very valuable resource. We study different noise sources, such as dephasing, phase flips, and bit flips in the quantum teleportation algorithm. We provide a taxonomy of the effects of the different noise sources on each qubit individually and together. To simulate the noise, we use the Lindblad master equation to allow for continuous error sources. We test both discrete and continuous error correction. This knowledge is used to develop more efficient error correction for the quantum teleportation algorithm; rather than correct every error on every qubit, we use limited resources to only correct the worst errors on the most sensitive qubits. |
Friday, March 9, 2018 9:48AM - 10:00AM |
X15.00010: Digital quantum simulator in the presence of a bath Yi-Cong Zheng For a digital quantum simulator (DQS) imitating a target system, we ask the following question: |
Friday, March 9, 2018 10:00AM - 10:12AM |
X15.00011: Density Matrix Simulation of 3 Qubit Quantum Error Correction Code Chungheon Baek, Yongsoo Hwang, Taewan Kim, Byung Choi Encoding logical qubits is the essential component for high performance quantum computer. Although 3-qubit bit-flip quantum error correction code cannot correct both bit-flip and phase-flip errors, it is a simple and small code because it employs cnot and toffoli gates without syndrome measurement and ancilla. This study examines how the accuracy of logical qubits is improved at the same computation time and how long the additional time is available for logical qubit gate operations. This density matrix model includes not only dephasing and relaxation process, but also gate and measurement errors. This simulation expected that the computation time of the logical qubits would be twice as long as the physical qubits with an accuracy of 95% if the entire time for quantum error correction is a hundredth of coherence time. The simulation results are compared with the IBM QX experiment as increasing the computation time for both physical and logical qubits. |
Friday, March 9, 2018 10:12AM - 10:24AM |
X15.00012: Demonstration of a Fault-Tolerant Error Syndrome Measurement: Theory Philip Reinhold, Serge Rosenblum, Mazyar Mirrahimi, Nissim Ofek, Liang Jiang, Luigi Frunzio, Michel Devoret, Robert Schoelkopf Fault tolerance is an essential ingredient in scaling up error corrected quantum computation. While all operations must eventually be made fault-tolerant, we focus here on syndrome measurement. It is particularly crucial to make this component as fault-tolerant as possible since it occurs frequently in all encoded circuits. Here we present a construction for the fault tolerant detection of an error syndrome, particularly the detection of photon number parity, which forms the foundation for error corrected logical qubits encoded in an oscillator. We introduce a modified parity measurement protocol using multiple ancilla levels. In contrast with previous schemes, this protocol can be protected to first order against ancilla decoherence occurring at any point in the sequence. |
Friday, March 9, 2018 10:24AM - 10:36AM |
X15.00013: Demonstration of a Fault-Tolerant Error Syndrome Measurement: Results Serge Rosenblum, Philip Reinhold, Mazyar Mirrahimi, Nissim Ofek, Liang Jiang, Luigi Frunzio, Michel Devoret, Robert Schoelkopf Forward propagation of ancilla errors onto logical qubits can counteract the effects of quantum error correction. Here, we show how in-situ control of the interaction Hamiltonian eliminates back-action of ancilla errors onto the logical qubit. We realize such an engineered interaction between a transmon ancilla and cavity-encoded logical qubit, and use it to implement a fault-tolerant photon-number parity measurement. We achieve a significant reduction of the error propagation rate compared to the non fault-tolerant implementation. This is a significant milestone towards fault-tolerant quantum computation, showing that fault tolerance can be implemented hardware-efficiently by exploiting physically relevant error models. |
Friday, March 9, 2018 10:36AM - 10:48AM |
X15.00014: Controlling electronic decoherence in quantum Hall edge channels Clément Cabart, Benjamin Roussel, Gwendal Fève, Pascal Degiovanni The recent developments of electron quantum optics in quantum Hall edge channels has opened the way to the development of quantum devices based on traveling single electron excitations. In particular, the development of single electron quantum tomography protocols based on two particle interferences has given us a new way to probe non linear electron quantum optics effects such as the ones induced by Coulomb interactions on single to few electron excitations propagating in ballistic quantum channels. In this talk, we discuss electronic decoherence through electron/hole pair creations in a single quantum Hall edge channel and show that a careful sample design can lead to decoherence control in the quantum Hall edge channel system at filling fraction two. We also discuss how such a specifically engineered interacting region could be used for single plasmon or single photon emission triggered by a single electron source. |
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