Conference

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Fault-Tolerant Quantum Computation with Constant Overhead

Daniel Gottesman University of Maryland, College Park

July 14, 2014

PIRSA:14070004
Spin glass reflection of the decoding transition for space-time codes

Alexey Kovalev University of California, Riverside

July 14, 2014

PIRSA:14070003
Maximum likelihood decoding threshold as a phase transition

Leonid Pryadko University of California, Riverside

July 14, 2014

PIRSA:14070002
Overview of the theory of spin glasses and its applications to quantum codes

Hidetoshi Nishimori Tokyo Institute of Technology

July 14, 2014

PIRSA:14070001
An introduction to quantum LDPC code

David Poulin Université de Sherbrooke

July 14, 2014

PIRSA:14070000
Free Discussion

June 19, 2014

PIRSA:14060038
Summary

Derek Jackson Kimball California State University, East Bay

June 19, 2014

PIRSA:14060037
Atomic magnetometers for precision measurements

Mike Romalis Princeton University

June 19, 2014

PIRSA:14060034
Nuclear spin precession of noble gases in ultra low magnetic fields

Lutz Trahms Physikalisch-Technische Bundesanstalt (PTB)

June 19, 2014

PIRSA:14060033
Optical magnetometry - From basics to Global Network of Optical Magnetometer for Exotic physics
- Nathan Leefer University of California, Berkeley
- Szymon Pustelny University of California, Berkeley
June 19, 2014

PIRSA:14060032
Free Discussion

June 18, 2014

PIRSA:14060031
Search for new physics in atoms: cosmic PNC and variation of alpha

Vladimir Dzuba University of New South Wales (UNSW)

June 18, 2014

PIRSA:14060030

Fault-Tolerant Quantum Computation with Constant Overhead

Daniel Gottesman University of Maryland, College Park

July 14, 2014

PIRSA:14070004

The threshold theorem for fault tolerance tells us that it is possible to build arbitrarily large reliable quantum computers provided the error rate per physical gate or time step is below some threshold value. Most research on the threshold theorem so far has gone into optimizing the tolerable error rate under various assumptions, with other considerations being secondary. However, for the foreseeable future, the number of qubits may be an even greater restriction than error rates. The overhead, the ratio of physical qubits to logical qubits, determines how expensive (in qubits) a fault-tolerant computation is. Earlier results on fault tolerance used a large overhead which grows (albeit slowly) with the size of the computation. I show that using quantum LDPC codes, it is possible in principle to do fault-tolerant quantum computation with low overhead, and with the overhead constant in the size of the computation.
Spin glass reflection of the decoding transition for space-time codes

Alexey Kovalev University of California, Riverside

July 14, 2014

PIRSA:14070003

We introduce space-time quantum code construction which is based on repeating the layers of an arbitrary quantum error correcting code. The error threshold of such space-time construction is shown to be related to the fault tolerant error threshold of the original quantum error correcting code in the presence of errors in syndrome measurements. The decoding transition for space-time codes can be further mapped to random-bond Wegner spin models.
Families of quantum low density parity-check (LDPC) codes with a finite decoding threshold lead to both known models (e.g., random bond Ising and random plaquette Z2 gauge models) as well as unexplored earlier and generally non-local disordered spin models with non-trivial phase diagrams that include the spin glass phase.
We apply this construction to the simplest examples of recently discovered hypergraph-product codes and numerically find the fault tolerant threshold in excess of 5% by employing Monte-Carlo simulations.
Maximum likelihood decoding threshold as a phase transition

Leonid Pryadko University of California, Riverside

July 14, 2014

PIRSA:14070002

In maximum likelihood (ML) decoding, we are trying to find the most likely error given the measured syndrome. While this is hardly ever practical, such a decoder is expected to have the highest threshold.
I will discuss the mapping between the ML threshold for an infinite family of stabilizer codes and a phase transition in an associated family of Ising models with bond disorder [1]. This is a generalization of the map between the toric codes and the square lattice Ising model. Quantum LDPC codes produce generally non-local spin models with few-body interactions. A relatively simple Monte Carlo simulation of such a model can give an upper bound on the decoding threshold for the original code family. This can be used to compare code families irrespectively of decoders, and to establish an absolute measure of decoder performance.

[1] A. A. Kovalev and L. P. Pryadko, "Spin glass reflection of the decoding transition for quantum error correcting codes," unpublished,
arXiv:1311.7688 (2013).
Overview of the theory of spin glasses and its applications to quantum codes

Hidetoshi Nishimori Tokyo Institute of Technology

July 14, 2014

PIRSA:14070001

I will review the theory of spin glasses with an emphasis on gauge symmetry. A number of exact results will be shown to be derived, some of which are useful to discuss the properties of quantum LDPC codes. Also will be explained is the combination of gauge symmetry, replica method, and duality argument to predict the precise location of a multicritical point, which is equivalent to the error-tolerance limit of toric code.
An introduction to quantum LDPC code

David Poulin Université de Sherbrooke

July 14, 2014

PIRSA:14070000

In this talk, I will cover some basic notions of quantum LDPC codes, focusing on the similarities and distinctions with their classical cousins. Topics will include definitions of stabilizer quantum LDPC codes (CSS and general), iterative decoding algorithms, dual spin models, and obstructions caused by error degeneracy. The talk will be informal and a good occasion to ask questions.
Free Discussion

June 19, 2014

PIRSA:14060038
Summary

Derek Jackson Kimball California State University, East Bay

June 19, 2014

PIRSA:14060037
Atomic magnetometers for precision measurements

Mike Romalis Princeton University

June 19, 2014

PIRSA:14060034

Atomic magnetometers have a long history in tests of Standard Model since they provide sensitive constraints on new spin interactions. I will review recent progress in magnetometry using electron and nuclear spins, describe some of the limits set on new physics and discuss ideas for future experiments.
Nuclear spin precession of noble gases in ultra low magnetic fields

Lutz Trahms Physikalisch-Technische Bundesanstalt (PTB)

June 19, 2014

PIRSA:14060033

In the low energy re¬gime, precision measurements of spin precession have gained increased attention as an alternative pathway to physics beyond the standard model. These measurements aim at the detection of minute frequency changes superimposed on low Larmor frequencies at extremely weak magnetic fields. Such measurements require an effective shielding against the magnetic field of the Earth and other perturbations. For measuring the precession frequency with high precision, a long lifetime of the precessing nuclear magnetization is required, thus the homogeneity of the applied field is a crucial parameter. In addition, criteria are needed that unambiguously distinguish magnetic artifacts from the non-magnetic exotic interactions that we search for. This can be accomplished by the concept of co-magnetometry, i.e., by simultaneous measuring the precession of two nuclear species such as 3He and 129Xe. Yet another kind of co-magnetometry is the use of SQUIDs for monitoring the spin precession. SQUIDs are magnetic field detectors of their own kind, which can measure the oscillating magnetic field generated by the precessing nuclear magnetic moment as well as the magnetic dc background field. In this presentation, I will report on the current state of the art in our lab in measurements of nuclear spin precession of noble gases.
Optical magnetometry - From basics to Global Network of Optical Magnetometer for Exotic physics
- Nathan Leefer University of California, Berkeley
- Szymon Pustelny University of California, Berkeley
June 19, 2014

PIRSA:14060032

In our talk we seek to present a broad overview of the field of optical magnetometers, starting from basic principles to fundamental limitations to the variety of applications in which they have already found use. We will end with a report on the development of a new worldwide network of synchronized magnetometers that can be used to search for a variety of new physical phenomena (many of which are discussed at this conference!).
Free Discussion

June 18, 2014

PIRSA:14060031
Search for new physics in atoms: cosmic PNC and variation of alpha

Vladimir Dzuba University of New South Wales (UNSW)

June 18, 2014

PIRSA:14060030

We consider pseudo-scalar and pseudo-vector interaction of atomic electrons with hypothetical dark matter particles (e.g., axions). These interactions lead to oscillating atomic parity non-conserving (PNC) amplitudes and/or oscillating electric dipole moments (EDM). In static
limit for PNC, existing atomic PNC experiments can be used to constrain time component of the pseudo-vector field.

Possible variation of fundamental constants is suggested by theories unifying gravity with other interactions. Evidence of the space/time variation of the fine structure constant alpha is found in
the quasar absorption spectra. Optical transitions in highly charged ions can be used as sensitive tools for studying time variation of alpha in laboratory.

Title	Speaker(s)	Date	Talk Type	Info link
Fault-Tolerant Quantum Computation with Constant Overhead	Daniel Gottesman	2014-07-14	Conference	View details
Spin glass reflection of the decoding transition for space-time codes	Alexey Kovalev	2014-07-14	Conference	View details
Maximum likelihood decoding threshold as a phase transition	Leonid Pryadko	2014-07-14	Conference	View details
Overview of the theory of spin glasses and its applications to quantum codes	Hidetoshi Nishimori	2014-07-14	Conference	View details
An introduction to quantum LDPC code	David Poulin	2014-07-14	Conference	View details
Free Discussion		2014-06-19	Conference	View details
Summary	Derek Jackson Kimball	2014-06-19	Conference	View details
Atomic magnetometers for precision measurements	Mike Romalis	2014-06-19	Conference	View details
Nuclear spin precession of noble gases in ultra low magnetic fields	Lutz Trahms	2014-06-19	Conference	View details
Optical magnetometry - From basics to Global Network of Optical Magnetometer for Exotic physics	Nathan Leefer, Szymon Pustelny	2014-06-19	Conference	View details
Free Discussion		2014-06-18	Conference	View details
Search for new physics in atoms: cosmic PNC and variation of alpha	Vladimir Dzuba	2014-06-18	Conference	View details

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