*Today: *
see Ramis's email for a talk starting shortly on tensor networks for spin
chains.
*Tuesday*
There is a seminar on generalizations of Haah's cubic code and implications
for topological order.
*CMT Informal Seminar
<http://web.mit.edu/physics/cmt/informalseminar.html>*Tuesday,
October 29, 2019 at 12:00 PM in 4-331
Meng Cheng, Yale University
"Exploring 3D fracton topological order: gauged layers construction and
entanglement renormalization"
There is also a talk on color centers in diamond.
*CUA Seminar
<http://www.rle.mit.edu/cua_responsive/event-type/cua-seminar-series/>*
Tuesday, October 29, 2019 at 4:00pm in MIT 4-270
Nathalie de Leon, Princeton
"Engineering coherent defects in diamond"
Ten Minute Talk: "Laser-cooled polyatomic molecules for precision
measurement" by Zack Lasner
*Wednesday*
I will speak at Harvard's "random matrix and probability" seminar at
3:15pm in the CMSA (20 Garden St) room G02.
http://cmsa.fas.harvard.edu/rm-and-pt/
My talk will be about my work on 2-D random circuits with Saeed as well as
John, Rolando, Alex Dalzell and Fernando Brandao.
*Thursday*
Opportunities and Challenges for Spin Qubits in Silicon
Ed Chen, HRL
6C-442, 12pm
Quantum information processing aims to leverage the properties of quantum
mechanics to manipulate information in ways that are not otherwise
possible. This would enable, for example, quantum computers that could
solve certain problems exponentially faster than a conventional
supercomputer. One promising approach for building such a machine is to use
gated silicon quantum dots. In the approach taken at HRL Laboratories,
individual electrons are trapped in a gated potential well at the barrier
of a Si/SiGe heterostructure. Spins on these electrons are compelling
candidates for qubits due to their long coherence times, all-electrical
control, and compatibility with conventional fabrication techniques. In
this talk, I will discuss our recent demonstrations of automated tune-up of
a six-dot Si device into a configuration suitable for high-fidelity,
randomized benchmarking of exchange-only qubits.
References:
1. RW Andrews et al. Nature Nanotechnology, 14 (8), 747-750 (2019)
2. AM Jones, et al. Physical Review Applied, 12 (1), 014026 (2019)
3. SM Meenehan (HRL). APS March Meeting, X34.00004 (2019)
You should all be on the iquise list, so you that you would also know about
their 3pm social on Thursday.
*Friday*
We will resume our group meetings and have a talk from Sultana Tokhy.
(11am, 6-310).
Title: Decoding Approximate Holographic Quantum Error Correcting Codes
Abstract: Holographic theories of quantum gravity are some of the most
successful marriages of quantum information theory and gravitational
physics. Most notably, the AdS/CFT (Anti de Sitter/Conformal Field Theory)
correspondence is a duality between a conformal field theory (CFT) in flat
spacetime and a theory of (quantum) gravity in one higher dimension. Since
the two theories are dual, all the information in the bulk spacetime can be
represented in one fewer dimension, reminiscent of an optical hologram.
Recently, AdS/CFT has been reinterpreted using the language of quantum
error correction. Toy models of these holographic quantum codes have been
proposed using tensor network models; one such network (known as the HaPPY
code) is based on the well-known 5 qubit code. Continuous variable analogs
of the HaPPY code have also been proposed, some of which have the property
of being U(1) covariant codes. Independently of AdS/CFT, it is known that
finite dimensional covariant codes cannot be perfectly error correcting,
and bounds on the quality of such a code have been placed. In this work, we
built simulations of both the 5 qubit HaPPY code and a U(1) covariant,
continuous variable generalization of the HaPPY code. Our simulation uses
the recently released TensorNetwork Python library. In addition to building
the holographic tensor network, we also implement explicit decoders for
each of the codes, as well as the so-called Petz map and twirled Petz map
recovery channels. We then compare the recovery fidelity using each of
these decoding methods to one another and, in the case of the covariant
codes, to the known bounds on the quality of approximate covariant codes.
Our results can help inform the development of more realistic, continuous
variable tensor network toy models of AdS/CFT.
In the afternoon (1:30pm, 6C-442) we will have a talk by Nicole Yunger
Halpern.
title: Noncommuting conserved charges in quantum many-body thermalization
In statistical mechanics, a small system exchanges conserved charges—heat,
particles, electric charge, etc.—with a bath. The small system may
thermalize to the canonical ensemble, or the grand canonical ensemble, etc.
The charges are usually represented by operators assumed implicitly to
commute with each other. But noncommutation distinguishes quantum physics
from classical. What if the operators fail to commute? A “non-Abelian
thermal state” was derived recently in the abstract, idealized framework of
quantum-information thermodynamics. Meanwhile, quantum many-body
thermalization has undergone a renaissance in high-energy physics;
condensed matter; and atomic, molecular, and optical physics: Toolkits
including the eigenstate thermalization hypothesis (ETH), random unitary
circuits, and out-of-time-ordered correlators have been developed. These
tools call for generalizing and application to nonclassically noncommuting
charges. We bridge noncommuting charges from quantum-information
thermodynamics to many-body physics: We extend the ETH, propose a protocol
for realizing the non-Abelian thermal state experimentally, and test the
protocol with numerical simulations of a spin chain. The protocol is suited
to ultracold atoms, trapped ions, and quantum dots. I will close with the
opportunities engendered for many-body physics by noncommuting charges.
*References*
NYH, Beverland, and Kalev, arXiv:1906.09227 (2019)
https://arxiv.org/abs/1906.09227.
NYH, Faist, Oppenheim, and Winter, Nat. Comms. 7, 12051 (2016)
https://www.nature.com/articles/ncomms12051.
NYH, J. Phys. A 51, 094001 (2018)
https://iopscience.iop.org/article/10.1088/1751-8121/aaa62f/meta.
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