CQT Anniversary
CQT's Anniversary Events

Join us online for a symposium commemorating thirteen years of CQT

In our tradition of celebrating the Centre for Quantum Technologies’ birthday with a scientific symposium, we invite you to join us online on 7 January 2021 for talks on quantum technologies by international experts. Everyone is welcome, and registration is free.

CQT was established in December 2007 as a Research Centre of Excellence in Singapore. The Centre does research in quantum communication and security, quantum computation and simulation, quantum sensing and metrology, as well as developing advanced instruments and pursuing basic science.

7 Jan 2021 Program
10:00am Ruth Kastner, University of Maryland
Quantum Paradoxes: A sign that we need to re-evaluate our ground rules
Arrow Abstract

Frauchiger and Renner have presented a heightened version of the Schrodinger’s Cat and Wigner’s Friend paradoxes that raise serious concerns about the coherence of quantum theory and especially about the apparently elusive notion of “measurement.” I propose that we regard this class of paradoxes as a symptom of a fundamental, but curable, problem afflicting the standard formulation of quantum theory. The problem arises because the standard formulation is based on deeply seated, but inappropriate, metaphysical and cultural ground rules that are identified and disclosed for critical review. The main ground rule critiqued is the idea that “real” quantum theory has no real, physical non-unitary dynamics. A specific counterexample is offered that does not require any ad hoc changes to the basic theory to force non-unitarity, but is based on a different theory of field behaviour in which non-unitarity naturally emerges.

11:00am Francesco Buscemi, Nagoya University
Fluctuation theorems from Bayesian retrodiction
Arrow Abstract

Quantitative studies of irreversibility in statistical mechanics often involve the consideration of a reverse process, whose definition has been the object of many discussions, in particular for quantum mechanical systems. Here we show that the reverse channel very naturally arises as Bayesian retrodiction, both in classical and quantum theories. Fluctuation relations then become expressions of the statistical divergence between the forward (i.e., predictive) and the reverse (i.e., retrodictive) process. With the reverse process constructed on consistent logical inference, rather than on particular balancing mechanisms in microscopic physics, fluctuation relations acquire a much broader form and scope. Previous paradigmatic results like Jarzynski's and Crooks' fluctuation relations are recovered as special cases. This is work in collaboration with Valerio Scarani.

12:00pm Howard Wiseman, Griffith University
Why experimental metaphysics needs a quantum computer

Arrow Abstract

Experimental metaphysics is the study of how empirical results can reveal indisputable facts about the fundamental nature of the world, independent of any theory. It is a field born from Bell’s 1964 theorem, and the experiments it inspired, proving the world cannot be both local and deterministic. However, there is an implicit assumption in Bell’s theorem, that the observed result of any measurement is absolute (it has some value which is not ‘relative to its observer’). This assumption may be called into question when the observer becomes a quantum system (the “Wigner’s Friend” scenario), which has recently been the subject of renewed interest. Here, building on work by Brukner, we derive a theorem, in experimental metaphysics, for this scenario [1]. It is similar to Bell’s 1964 theorem but dispenses with the assumption of determinism. The remaining assumptions, which we collectively call "local friendliness", yield a strictly larger polytope of bipartite correlations than those in Bell's theorem (local determinism), but quantum mechanics still allows correlations outside the local friendliness polytope. We illustrate this in an experiment in which the friend system is a single photonic qubit [1]. I argue that a truly convincing experiment could be realised if that system were a sufficiently advanced artificial intelligence software running on a very large quantum computer, so that it could be regarded genuinely as a friend. I will briefly discuss the implications of this far-future scenario for various interpretations and modifications of quantum theory.

[1] Kok-Wei Bong, Aníbal Utreras-Alarcón, Farzad Ghafari, Yeong-Cherng Liang, Nora Tischler, Eric G. Cavalcanti, Geoff J. Pryde and Howard M. Wiseman, “A strong no-go theorem on the Wigner’s friend paradox", Nature Physics (2020).

1:00pm Break
2:30pm Gil Kalai, Hebrew University of Jerusalem
Statistical, mathematical, and computational aspects of noisy intermediate-scale quantum computers
Arrow Abstract

Noisy intermediate-scale quantum (NISQ) Computers hold the key for important theoretical and experimental questions regarding quantum computers. In the lecture I will describe some questions about statistics, mathematics, and computational complexity which arose in my study of NISQ systems and are related to
a) My general argument "against" quantum computers,
b) My analysis (with Yosi Rinott and Tomer Shoham) of the Google 2019 "quantum supremacy" experiment.

Relevant papers:
Yosef Rinott, Tomer Shoham and Gil Kalai, Statistical aspects of the quantum supremacy demonstration, https://gilkalai.files.wordpress.com/2019/11/stat-quantum2.pdf Gil Kalai, The Argument against Quantum Computers, the Quantum Laws of Nature, and Google’s Supremacy Claims, https://gilkalai.files.wordpress.com/2020/08/laws-blog2.pdf Gil Kalai, Three puzzles on mathematics, computations, and games, https://gilkalai.files.wordpress.com/2019/09/main-pr.pdf

3:30pm Markus Aspelmeyer, IQOQI Vienna, University of Vienna
Quantum optical control of levitated solids: a fresh perspective on the gravity-quantum interface
Arrow Abstract

The increasing level of control over motional quantum states of massive, solid-state mechanical devices opens the door to an hitherto unexplored parameter regime of macroscopic quantum physics. I will report on our recent progress towards controlling levitated solids in the quantum regime. I will discuss the prospects of using these systems for fundamental tests of physics, including the interface between quantum and gravitational physics.

4:30pm Closing remarks by José Ignacio Latorre CQT, NUS
5:00pm End of Symposium

Time shows in Singapore time (GMT +8).
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