Quantum Optics Seminar by Andrew White – University of Copenhagen

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Quantum Optics Seminar by Andrew White

Lift Abstract: We review photonic quantum simulation, its use in biology, chemistry, computer science and physics, and its prospects for scaling given the latest advances in quantum photonics, notably in sources, detectors, and nonlinear interactions.

Stuck-in-the-lift Abstract:

In principle, quantum mechanics can exactly describe *any* system of quantum particles—from simple molecules to unwieldy proteins—but in practice this is impossible as the number of equations grows exponentially with the number of particles. 

A well known example is the fundamental problem faced in quantum chemistry, calculating molecular properties such as total energy of the molecule. In principle this is done by by solving the Schrödinger equation; in practice the computational resources required increase exponentially with the number of atoms involved and so approximations become necessary. Recognising this, in 1982 Richard Feynman suggested using quantum components for such calculations [1]. It wasn't until the 1990's than a quantum algorithm was proposed where the computational resources increased only polynomially in the problem size [2], and experimental implementations are even more recent, e.g. a photonic quantum computer was used in 2010 to obtaining the energies—at up to 47 bits of precision—of the hydrogen molecule, H2 [3]. 

Here we examine the state of play in photonic quantum simulation, highlighting the difference between wave-mechanics simulations, which can be done with single photons or classical light, and quantum-mechanics simulations, which require multiple photons. Along the way we look at phenomena and problems from biology, chemistry, computer science, and physics, including zitterbewegung, enhanced quantum transport, quantum chemistry, and topological phases. We discuss the latest advances in photon technology, notably sources [4] detectors, and nonlinear interactions, and the implications for large-scale implementations in the near to medium term, e.g. in the BosonSampling problem [5,6]. 

[1]. R. P. Feynman, International Journal of Theoretical Physics 21, 467–488 (1982).[2]. S. Lloyd, Science 273, 1073–1078 (1996)
[3]. B. P. Lanyon, J. D. Whitfield, G. G. Gillet, M. E. Goggin, M. P. Almeida, I. Kassal, J. D. Biamonte, M. Mohseni, B. J. Powell, M. Barbieri, A. Aspuru-Guzik and A. G. White, Nature Chemistry 2, 106 (2010).
[4]. O. Gazzano, M. P. Almeida, A. K. Nowak, S. L. Portalupi, A. Lemaître, I. Sagnes, A. G. White, and P. Senellart, Physical Review Letters 110, 250501 (2013).
[5]. S. Aaronson and A. Arkhipov, Proceedings of the ACM Symposium on Theory of Computing, San Jose, CA pp. 333–342 (2011).
[6]. M. A. Broome, A. Fedrizzi, S. Rahimi-Keshari, J. Dove, S. Aaronson, T. C. Ralph, and A. G. White, Science 339, 794 (2013). 

Bio:

Andrew was raised in a Queensland dairy town, before heading south to the big smoke of Brisbane to study chemistry, maths, physics and—during World Expo 88—the effects of alcohol on uni students from around the world. Deciding he wanted to know what the cold felt like, he first moved to Canberra, then Germany—completing his PhD in quantum physics—before moving on to Los Alamos National Labs in New Mexico