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We'd like to announce the next Q+ hangout.  As usual, please leave a comment below if you would like to join the hangout itself.  Everyone else can watch on the livestream.

Title: Fault-tolerant quantum computation with constant overhead

Abstract: 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 even larger (albeit slowly) with the size of the computation. I show that it is possible in principle to do fault-tolerant quantum computation with the overhead constant in the size of the computation, and with a low constant at that. The result depends on recent progress on quantum low-density parity check codes.
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Q+ Hangout: Daniel Gottesman (Perimeter Institute)
Tue, May 20, 9:00 AM
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Zhangqi Yin's profile photoRavi Kunjwal's profile photoQ+'s profile photoMatthew Leifer's profile photo
8 comments
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+Chris Richardson, OK you are in for now, but if we get oversubscribed and you are not there 5min before the talk then I will reopen your seat.
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Since we don't have many group reservations, we are opening up the possibility of booking a seat in the hangout to individuals, particularly those who work on related areas and might have good questions for Tobias.  If you are an individual who would like to be in the hangout rather than just watching the livestream then please comment below.
 
We'd like to announce the next Q+ hangout.  As usual, if you are watching with a group and want to reserve a seat in the hangout then leave a comment on the event page.  Everyone else can watch on the livestream.

Title: A Combinatorial Approach to Nonlocality and Contextuality

Abstract:
Most work on contextuality so far has focused on specific examples and concrete proofs of the Kochen-Specker theorem, while general definitions and theorems about contextuality are sparse. For example, it is commonly believed that nonlocality is a special case of contextuality, but what exactly does this mean? After a brief discussion of previous work, I will introduce our "device-independent" approach to contextuality based on the mathematics of test spaces and explain how nonlocality is indeed a special case of contextuality. This work builds on the graph-theoretic approach of Cabello, Severini and Winter by improving on several of its shortcomings and merging it with the work of Foulis and Randall on test spaces. Our results include:

(1) various relationships to graph invariants, similar to CSW;
(2) a proof that our set of quantum models cannot be characterized by a graph invariant;
(3) a proof that the set of all models satisfying the Consistent Exclusivity principle at any number of copies is not convex;
(4) new results on the Shannon capacity of graphs;
(5) an "inverse sandwich conjecture" with ramifications for C*-algebra theory and quantum logic.

This talk is based on http://arXiv.org/abs/1212.4084
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Q+ Hangout: Tobias Fritz (Perimeter Institute)
Tue, March 25, 10:00 AM
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Elie Wolfe's profile photoQ+'s profile photo
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OK, +Elie Wolfe.  You are in.
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Title: Dimension of Physical Systems

Abstract:
The dimension of a physical system refers loosely speaking to the number of degrees of freedom relevant to describe it. Here we ask how quantum theory compares to more general models (such as Generalized Probabilistic Theories) from the point of view of dimension. This gives insight to information processing and thermodynamics in GPTs.
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Q+ Hangout: Nicolas Brunner
Tue, February 25, 1:30 PM
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Video from today's hangout by +Troels Frimodt Rønnow  now online Q+: Troels Frimodt Rønnow
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Q+: Troels Frimodt Rønnow
Tue, January 28, 8:45 AM
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Marco Carvalho's profile photoQ+'s profile photo
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Go to
https://plus.google.com/events/ceopiisgb21l18icajq0b4c6lnk to see the video.


We'd like to invite you to the next Q+ hangout with Troels Frimodt Rønnow from ETH Zurich.

TITLE: Quantum annealing on 503 qubits

ABSTRACT: Quantum speedup refers to the advantage of quantum devices can  over classical ones in solving  classes of computational problems. In this talk we show how to correctly define and measure quantum speedup in experimental devices. We show how to avoid issues that might mask or fake quantum speedup. As illustration we will compare the performance of a D-Wave Two quantum annealing device on random spin glass instances to simulated classical and quantum annealers, and other classical solvers.

If you are sharing this talk with a group of people, you can reserve a seat in the hangout in the thread below. Otherwise, simply go to the event page  https://plus.google.com/events/c7prl3ob61i2cr6sglu5s0tmm0c at the above date/time, and you will see a livestream there.
11
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Jérémie Roland's profile photoQ+'s profile photoInformation, Computation, Intelligence and Quantum's profile photoMatthew Leifer's profile photo
15 comments
 
Has anything started yet?
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Q+

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We'd like to announce the next Q+ hangout.  As usual, if you are watching with a group and want to reserve a seat in the hangout then leave a comment.  Otherwise you can watch on the livestream.

Title: On the Uncertainty of the Ordering of Nonlocal Wavefunction Collapse when Relativity is Considered

Abstract: The temporal measurement order and therefore the originator of the instantaneous collapse of the wavefunction of a spatiality entangled particle pair can change depending on the reference frame of an observer. This can lead to a paradox in which its seems that both measurements collapsed the wavefunction before the other. We resolve this paradox by demonstrating how attempting to determine the order of measurement of the entangled pair introduces uncertainty which makes the measurement order impossible to know.
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Q+ Hangout: Chris Richardson (University of Liege)
Tue, April 22, 9:00 AM
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Ravi Kunjwal's profile photoQ+'s profile photoInformation, Computation, Intelligence and Quantum's profile photoMatthew Leifer's profile photo
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+Ravi Kunjwal OK done
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We'd like to announce the next Q+ hangout.  As usual, if you are watching with a group and want to reserve a seat in the hangout then leave a comment on the event page.  Everyone else can watch on the livestream.

Title: A Combinatorial Approach to Nonlocality and Contextuality

Abstract:
Most work on contextuality so far has focused on specific examples and concrete proofs of the Kochen-Specker theorem, while general definitions and theorems about contextuality are sparse. For example, it is commonly believed that nonlocality is a special case of contextuality, but what exactly does this mean? After a brief discussion of previous work, I will introduce our "device-independent" approach to contextuality based on the mathematics of test spaces and explain how nonlocality is indeed a special case of contextuality. This work builds on the graph-theoretic approach of Cabello, Severini and Winter by improving on several of its shortcomings and merging it with the work of Foulis and Randall on test spaces. Our results include:

(1) various relationships to graph invariants, similar to CSW;
(2) a proof that our set of quantum models cannot be characterized by a graph invariant;
(3) a proof that the set of all models satisfying the Consistent Exclusivity principle at any number of copies is not convex;
(4) new results on the Shannon capacity of graphs;
(5) an "inverse sandwich conjecture" with ramifications for C*-algebra theory and quantum logic.

This talk is based on http://arXiv.org/abs/1212.4084
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Q+ Hangout: Tobias Fritz (Perimeter Institute)
Tue, March 25, 10:00 AM
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Ben Rogers's profile photoRavi Kunjwal's profile photoQ+'s profile photoMatthew Leifer's profile photo
7 comments
 
If there are any spots left, I'd like one for the theory group in Geneva
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***FOR THE LIVE VIDEO STREAM GO HERE: https://plus.google.com/events/c8qnklo1cuv48l5cnjmajnv2tak

We'd like to announce the next Q+ hangout.  As usual, if you are watching with a group and would like to reserve a seat in the hangout then leave a comment.  Everyone else can watch on the livestream on the event page.

Title: Dimension of Physical Systems

Abstract:
The dimension of a physical system refers loosely speaking to the number of degrees of freedom relevant to describe it. Here we ask how quantum theory compares to more general models (such as Generalized Probabilistic Theories) from the point of view of dimension. This gives insight to information processing and thermodynamics in GPTs.
Q+ Hangout: Nicholas Brunner (University of Geneva)
Tue, February 25, 11:00 AM EST
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Ravi Kunjwal's profile photoQ+'s profile photoInformation, Computation, Intelligence and Quantum's profile photoMatthew Leifer's profile photo
20 comments
 
Thanks for the great talk. 
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Hangout starting in 10 minutes!
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Q+: Troels Frimodt Rønnow
Tue, January 28, 8:45 AM
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This is a reminder for tomorrows Q+ hangout with Troels Frimodt Rønnow from ETH Zurich. We still have two reservation seats free so if you'd like to actively join with your webcam let us know below. Otherwise, simply go to the event page  https://plus.google.com/events/c7prl3ob61i2cr6sglu5s0tmm0c tomorrow (Tuesday) at 14:00 and you will see a livestream there.

TITLE: Quantum annealing on 503 qubits

ABSTRACT: Quantum speedup refers to the advantage of quantum devices can  over classical ones in solving  classes of computational problems. In this talk we show how to correctly define and measure quantum speedup in experimental devices. We show how to avoid issues that might mask or fake quantum speedup. As illustration we will compare the performance of a D-Wave Two quantum annealing device on random spin glass instances to simulated classical and quantum annealers, and other classical solvers.
2
Rong Zhou's profile photoElie Wolfe's profile photoCharles Clark's profile photoQ+'s profile photo
5 comments
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+Elie Wolfe , there was another request from Leeds so I have given plurality priority. Thanks anyway, we'll try to get the 15 seats option activated soon which makes space for individuals to join.
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#hangoutsonairDaniel Burgarth, Mark Wilde, Aharon Brodutch, and Mark Girard
Q+ answered questions from audience
Q+ Hangout: Mark Wilde
Q+ and 4 others participated
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In their circles
3,158 people
Have them in circles
2,885 people
Manish kumar Choudhary's profile photo
J.F. Vega's profile photo
Ulises M. Alvarez's profile photo
Trone Miller's profile photo
Douglas Kaapana's profile photo
Tycko Franklin's profile photo
Richard Green's profile photo
Manuel Escamilla's profile photo
Ronald Rendell's profile photo
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Q+ hangouts: international online seminars and discussions on quantum theory
Introduction
Q+ is a series of online seminars on quantum information and quantum foundations that use Google+ hangouts.  Seminars currently happen once a month and are organized by Daniel Burgarth and Matthew Leifer.

Follow this page for seminar announcements and to see the hangout.
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