Tag Archives: talks

The Many Worlds of Quantum Mechanics

Posted on 29 August, 2020 by | Leave a comment

This post exists because many people have complained that the link pointed to a dummy website rather than a page with details of the event. There are no more details of the event other than what you have already seen on Twitter, Facebook, etc. or the email you received. The link will point directly to the YouTube livestream on the day of the event rather than here. I will also post the livestream link here once it has been set up in case anyone bookmarks this page by mistake.

Sean Carroll

The Many Worlds of Quantum Mechanics
A Popular Physics Discussion
Sean Carroll in conversation with Matt Leifer
Wednesday September 16, 5pm PDT (California Time)

The Institute for Quantum Studies at Chapman University presents an online discussion between Dr. Sean Carroll (Caltech) and Dr. Matthew Leifer (co-Director of the Institute for Quantum Studies at Chapman) on the many-worlds interpretation of quantum mechanics.  Dr. Carroll is a theoretical physicist, specializing in quantum mechanics, gravitation, cosmology, statistical mechanics, and foundations of physics.  He is also a prolific author of popular science book and his latest – Something Deeply Hidden: Quantum Worlds ad the Emergence of Spacetime – argues that quantum mechanics is best explained in terms of multiple universes that are constantly splitting from one another, and explains how this point of view may help us to understand quantum gravity.  This will be the topic of conversation with Dr. Leifer, which will be accessible to a general audience.  The conversation will be broadcast live on YouTube at There will be an opportunity for audience Q&A and a book giveaway during the event.

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Q+ Hangout Lorenzo Maccone

Posted on 3 June, 2015 by | 1 comment

Here are the details of the next Q+ Hangout.

Speaker: Lorenzo Maccone (Universita’ di Pavia)
Date/time: Tuesday 9th June 2015, 2pm BST
Title: Quantum Time

Abstract:
We give a consistent quantum description of time, based on Page and Wootters’ conditional probabilities mechanism, that overcomes the criticisms that were raised against similar previous proposals. In particular we show how the model allows to reproduce the correct statistics of sequential measurements performed on a system at different times.

This is joint work with Vittorio Giovannetti and Seth Lloyd and
is based on arXiv:1504.04215.

To watch the talk live, visit the event page at the appointed hour.

To keep up to date on the latest news about Q+ hangouts you can follow us on:

or visit our website at http://qplus.burgarth.de

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Q+ Hangout: Howard Wiseman

Posted on 20 November, 2014 by | Leave a comment

Here are the details of the next Q+ hangout.

Date/time: Wed. 26th Nov. 2014 10pm GMT/UTC

Speaker: Howard Wiseman (Griffith University)

Title: After 50 years, Bell’s Theorem Still Reverberates

Abstract:
Fifty years ago this month, Belfast-born physicist John Bell submitted for publication a paper [1] which has been described as “the most profound discovery in science” [2]. However, its significance is still much disputed by physicists and philosophers [3, 4].
I will explain what is so puzzling about the types of correlations Bell introduced, by a specific example based on [5]. (For those well-versed in Bell inequalities this may still be of pedagogical interest.)
But what exactly do these Bell-type correlations violate? Bell’s original answer [1] was the joint assumptions of determinism and locality. His later answer [6] was the single assumption of local causality (which, confusingly, he sometimes also called locality). Different ‘camps’ of physicists – operationalists and realists respectively – prefer the different versions of Bell’s theorem.

Which of Bell’s notions, locality or local causality, expresses the causal structure of Einstein’s theory of relativity? I will argue for the answer: neither [3,4]. Both notions require an additional causal assumption, and the one required for local causality is a stronger one. I will discuss how the different assumptions fit with the ideologies of the two camps, and how they can best be reconciled.

[1]  J. S. Bell, “On the Einstein-Podolsky-Rosen paradox”, Physics 1, 195-200 (1964).
[2]  H. P. Stapp, “Are superluminal connections necessary?”, Nuovo Cim. 40B, 191 (1977).
[3]  H. M. Wiseman, “The two Bell’s theorems of John Bell”, J. Phys. A 47, 424001 (2014) (Invited Review for Special Issue, 50 years of Bell’s theorem)
[4]  H. M. Wiseman, “Bell’s theorem still reverberates”, Nature 510, 467-9 (2014).
[5] P. K. Aravind, “Bell’s theorem without inequalities and only two distant observers”,  Found. Phys. Lett. 15, 397 (2002).
[6]  J. S. Bell, “The Theory of Local Beables”, Epistemological Lett. 9, 11-24 (1976).

To watch the talk live, visit the event page at the appointed hour.

To keep up to date on the latest news about Q+ hangouts, you can follow us on:

or visit our website.

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Q+ Hangout: Marco Piani

Posted on 15 October, 2014 by | Leave a comment

Here are the details of the next Q+ hangout:

Date: Monday 27th October 2pm GMT/UTC

Spekaer: Marco Piani (University of Strathclyde)

Title: Usefulness of entanglement and steering in the discrimination of physical processes

Abstract: Not all entangled states are created equal: they are all special, but some are more special than others. In particular, this is true in an operational characterization of quantum correlations based on their usefulness in the discrimination of physical processes. We will discuss how every entangled state of a probe-ancilla composite system is useful as a resource for the problem of minimum-error channel discrimination. We will then focus on the subset of entangled states that exhibit steering. The latter is the entanglement-based quantum effect that embodies the “spooky action at a distance” disliked by Einstein and scrutinized by Einstein, Podolsky, and Rosen. We prove that, for any fixed steerable state, there are instances of a generalization of the channel discrimination problem, which we dub quantum subchannel discrimination, where such a state allows a correct discrimination with strictly higher probability than in absence of entanglement, even when measurements are restricted to local measurements aided by one-way communication. On the other hand, unsteerable states are useless under such a restriction, even when entangled. We also prove that the above steering advantage can be exactly quantified in terms of the steering robustness, which is a natural measure of the steerability exhibited by the state.
This talk is based on joint work with J. Watrous, arXiv:1406.0530.

To watch live, visit the hangout page at the appointed hour.

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Q+ Hangout: Daniel Gottesman

Posted on 6 May, 2014 by | Leave a comment

Here are the details of the next Q+ hangout. To watch live, visit this link at the appointed hour.

Date/time: Tue. May 20th 2014 2pm BST/UTC+1

Speaker: Daniel Gottesman (Perimeter Institute)

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.

To keep up to date on the latest news about Q+ hangouts you can follow us on:

or visit our website.

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Q+ hangout: Chris Richardson

Posted on 8 April, 2014 by | Leave a comment

Here are the details of the next Q+ hangout.

Date/time: 22nd April 2014 2pm BST/UTC+1

Speaker: Chris Richardson (University of Liege)

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.

To watch the talk live, go to the event page at the appointed hour.

To keep up to date on the latest news about Q+ hangouts you can follow us on:

or visit our website.

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Q+ Hangout: Tobias Fritz

Posted on 11 March, 2014 by | Leave a comment

Here are the details of the next Q+ hangout. To watch live, visit the event page at the appointed hour. Be aware of the fact that although North America has switched to DST, the UK has not yet and the time is still listed in GMT/UTC.

Date/time: Tuesday 25th March 2014 2pm GMT/UTC

Speaker: Tobias Fritz (Perimeter Institute)

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 arXiv:1212.4084.

To keep up to date with the latest news about Q+ hangouts you can follow us on:

or visit our website.

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Q+ Hangout: Nicholas Brunner

Posted on 11 February, 2014 by | Leave a comment

Here are the details of the next Q+ hangout.

Date/time: Tue. 25th Feb. at 4pm GMT/UTC

Speaker: Nicholas Brunner (University of Geneva)

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.

To watch the talk live, visit the event page at the appointed hour.

To keep up to date on the latest news about Q+ hangouts you can follow us on:

or visit our website http://qplus.burgarth.de

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Q+ Hangout: Troels Frimodt Rønnow

Posted on 15 January, 2014 by | Leave a comment

Here are the details of the next Q+ hangout

Date: 28th January 2014

Time: 2pm UTC/GMT

Speaker: Troels Frimodt Rønnow (ETH Zurich)

Title: Quantum annealing on 503 qubits

Abastract: 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.

To watch the talk live go to http://gplus.to/qplus at the appointed hour.

To keep up to date on the latest news about Q+ hangouts you can follow us on:

or visit our website at http://qplus.burgarth.de

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Q+ Hangout: Mark Wilde

Posted on 12 November, 2013 by | Leave a comment

Here are the details of the next Q+ hangout.

Date/time: Tue. 26th Nov. 3pm GMT/UTC

Speaker: Mark Wilde (Louisiana State University)

Title: Strong Converse Theorems in Quantum Information Theory

Abstract: One of the main goals in quantum information theory is to establish the capacity of a quantum channel for communicating various kinds of information, whether it be bits or qubits. While several communication capacities of quantum channels are now known, the characterization of capacity in many of these cases is often limited to it being a threshold that determines the rates at which reliable communication is or is not possible. While this characterization might be satisfactory for some purposes, it leaves open the possibility for a trade-off between communication rate and error probability (that is, one might think that it would be possible to send data at a higher rate by allowing for errors to occur some of the time). However, we now know that such a trade-off is not possible for many channels and capacities of interest. That is, many researchers have now established that a strong converse theorem holds for several channels and capacities, so that as soon as the communication rate exceeds capacity, it is guaranteed that the error probability converges to one in the limit of large blocklength, no matter what strategy the sender and receiver employ. These strong converse theorems strengthen the interpretation and our understanding of capacity as a very sharp dividing line between rates for which asymptotically perfect communication is possible and rates for which an error is guaranteed to occur (analogous to a phase transition in statistical physics). This Q+ talk will review much of the progress in establishing strong converse theorems for several channels and their communication capacities in quantum information theory.

Joint work with Bhaskar Roy Bardhan (LSU Baton Rouge), Manish K. Gupta (LSU Baton Rouge), Naresh Sharma (TIFR Mumbai), Dong Yang (UAB Barcelona), and Andreas Winter (UAB Barcelona).

To watch the talk live, go to http://gplus.to/qplus at the appointed hour. To stay up to date on the latest news about Q+ hangouts you can follow us on:

or visit our website http://qplus.burgarth.de

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