Quantum photo-thermodynamics on a programmable photonic quantum processor

One of the core questions of quantum physics is how to reconcile the unitary evolution of quantum states, which is information-preserving and time-reversible, with the second law of thermodynamics, which is neither. The resolution to this paradox is to recognize that global unitary evolution of a multi-partite quantum state causes the state of local subsystems to evolve towards maximum-entropy states. In this work, we experimentally demonstrate this effect in linear quantum optics by simultaneously showing the convergence of local quantum states to a generalized Gibbs ensemble constituting a maximum-entropy state under precisely controlled conditions, while using a new, efficient certification method to demonstrate that the state retains global purity. Our quantum states are manipulated by a programmable integrated photonic quantum processor, which simulates arbitrary non-interacting Hamiltonians, demonstrating the universality of this phenomenon. Our results show the potential of photonic devices for quantum simulations involving non-Gaussian states

Shih-Alley entanglement generation in physical unclonable keys

Secure communication is of crucial importance for many applications. Currently communication security is based on encryption protocols which are computationally hard to crack by classical computers. However, it is generally believed that quantum computers will be able to decipher these encryption methods. Quantum communication has to potential to solve this threat, but it is vulnerable to man-in-the-middle attacks. Recently, Goorden et al. proposed a scheme which uses a multiple-scattering key as an authentication device, which solves the man-in-the-middle threat.[1] As a next step towards secure quantum communication we propose a Shih-Alley type of entanglement generation in such a scattering key.[2] This would enable us to develop a one-sided device-independent communication protocol. We report on the latest developments in this experiment. [1] S.A. Goorden et al., Optica 1, 421-424 (2014) [2] Y.H. Shih et al., Phys. Rev. Lett. 61, 2921 (1988

Optimizing spontaneous parametric down-conversion sources for boson sampling

An important step for photonic quantum technologies is the demonstration of a quantum advantage through boson sampling. In order to prevent classical simulability of boson sampling, the photons need to be almost perfectly identical and almost without losses. These two requirements are connected through spectral filtering, improving one leads to a decrease of the other. A proven method of generating single photons is spontaneous parametric downconversion (SPDC). We show that an optimal trade-off between indistinguishability and losses can always be found for SPDC. We conclude that a 50-photon scattershot boson-sampling experiment using SPDC sources is possible from a computational complexity point of view. To this end, we numerically optimize SPDC sources under the regime of weak pumping and with a single spatial mode