Program
Full Program | Thursday | Friday | Saturday | All Sessions | Posters | Talks
LSU SQuInT Event Map
SESSION 9a: Quantum error correction and prevention (JC Miller Hall, Rm 134)Chair: (Todd Brun (Southern California)) | |
| 3:45pm - 4:15pm | Theodore Yoder, MIT The surface code with a twist | Abstract. The surface code is one of the most successful approaches to topological quantum error-correction. It boasts the smallest known syndrome extraction circuits and correspondingly largest thresholds. Defect-based logical encodings of a new variety called twists have made it possible to implement the full Clifford group without state distillation. Here we investigate a patch-based encoding involving a modified twist. In our modified formulation, the resulting codes, called triangle codes for the shape of their planar layout, have only weight-four checks and relatively simple syndrome extraction circuits that maintain a high, near surface-code-level threshold. They also use 25% fewer physical qubits per logical qubit than the surface code. Moreover, benefiting from the twist, we can implement all Clifford gates by lattice surgery without the need for state distillation. By a surgical transformation to the surface code, we also develop a scheme of doing the same gates on surface code patches in an atypical planar layout, though with less qubit efficiency than the triangle code. Finally, we remark that logical qubits encoded in triangle codes are naturally amenable to logical tomography, and the smallest triangle code can demonstrate high-pseudothreshold fault-tolerance to depolarizing noise using just 13 physical qubits. |
| 4:15pm - 4:45pm | Aleksander Kubica, IQIM, Caltech Three-dimensional color code thresholds via statistical-mechanical mapping | Abstract. The color code is an example of a topological quantum error-correcting code which recently has gained a lot of attention due to achieving universality without magic-state distillation in three dimensions. Also, the color code illustrates a new and exciting idea of single-shot error correction which might drastically reduce time overhead of quantum computation. In this work we find fundamental bounds on the error-correcting capabilities of the three-dimensional color code, namely the threshold for optimal error correction of bit-flip/phase-flip noise with perfect measurements on the body-centered cubic lattice. In particular, the threshold associated with string-like (one- dimensional) and sheet-like (two-dimensional) logical operators is p_1 ≃ 1.9% and p_2 ≃ 27.5%, respectively. The aforementioned results were obtained by exploiting a connection between error correction and statistical mechanics. We performed parallel tempering Monte Carlo simulations of two previously unexplored three-dimensional statistical-mechanical models: the 4-body and the 6- body random coupling Ising models. We find their phase diagrams in terms of disorder strength and temperature. Our results put constraints on the practical use of the color code from the viewpoint of efficient decoders and bounding overhead. |
| 4:45pm - 5:15pm | Haoyu Qi, Louisiana State Optimal digital dynamical decoupling for general decoherence via Walsh modulation | Abstract. We provide a general framework for constructing digital dynamical decoupling sequences based on Walsh modulation, applicable to arbitrary qubit decoherence scenarios. Building on the equivalence between the Walsh formalism and the recently introduced concatenated-projection approach, we identify a family of optimal Walsh sequences which can be exponentially more efficient, in terms of the required total pulse number for fixed cancellation order, than known sequences based on concatenated design. Optimal sequences for a given cancellation order are highly non-unique, their performance depending sensitively on the control path. We provide an analytical upper bound to the achievable decoupling error, and argue how suitable path-optimized sequences within the optimal Walsh family can substantially outperform concatenated decoupling, while respecting realistic timing constraints. We validate these conclusions by numerically computing the average fidelity in a toy model capturing the essential feature of hyperfine-induced decoherence in a quantum dot. |
| 5:15pm - 5:45pm | Ryan Epstein, Northrop Grumman Protecting quantum information from noise -- a passive approach | Abstract. The steady improvement in coherence times and gate fidelities over the past several years has largely been due to reductions in noise and energy loss mechanisms. Achieving highly integrated quantum hardware, however, may necessitate tolerance of noisier signals and dirtier materials. Over the past couple of years, we have been looking at practical ways to design noise-resilience into quantum devices. In this talk, I’ll present theoretical work on methods for performing gates that are robust to control noise and that reduce qubit overhead and coupling complexity, building off of Bacon and Flammia’s Adiabatic Gate Teleportation technique. I’ll also talk about more fully noise-protected qubits and gates using blocks of qubits coupled together in Bacon-Shor-like codes. |
| 5:45pm - 6:15pm | Sepehr Nezami, Stanford Quantum error correction of reference frame information | Abstract. The existence of quantum error correcting codes is one of the most counterintuitive and potentially technologically important discoveries of quantum information theory. But standard error correction refers to abstract quantum information, i.e. information that is independent from the physical incarnation of the systems used for storing the information. There are, however, other forms of information that are physical, one of the most ubiquitous being reference frame information. Here we analyze the problem of error correcting physical information. The basic question we seek to answer is whether such error correction is possible, and, if yes, the limitations to which it is subjected. The issue is highly nontrivial given the fact that the systems that need to be used for transmitting physical information must contain the physical quantity we are interested in, so all actions applying to them, including the encoding/decoding necessary for error correction, are subjected to limiting constraints. |
SQuInT Chief Organizer
Akimasa Miyake, Assistant Professor
amiyake@unm.edu
SQuInT Co-Organizer
Mark M. Wilde, Assistant Professor LSU
mwilde@phys.lsu.edu
SQuInT Administrator
Gloria Cordova
gjcordo1@unm.edu
505 277-1850
SQuInT Event Coordinator
Karen Jones, LSU
kjones@cct.lsu.edu
SQuInT Founder
Ivan Deutsch, Regents' Professor
ideutsch@unm.edu
