Discrete-time quantum walks (DTQWs) are ideal model systems to explore quantum transport phenomena involving the delocalization of pseudo-spin-1/2 particles on a lattice. The repeated application of the coin operation coherently coupling the internal spin states and of spin-dependent shift operations defines the simplest type of discrete-time quantum walk. Additional unitary operations added to the definition of the single step permit to simulate the effect of both electric and magnetic fields acting on a charged particle.

I will report on quantum walk experiments employing ultracold Caesium atoms trapped in polarisation-synthetized optical lattices. Polarisation-synthetized optical lattices represent a conceptually new realization of spin-dependent optical lattices, promising a wide range of applications in ultracold atom experiments beyond quantum walk experiments. Atoms in spin-up and spin-down states are trapped by two fully independent optical lattices whose position and depth can be individually controlled in time. The residual jitter between the two lattices is on the order of 1Å. We made use of this system to implement ideal negative measurements of spin states demonstrating a 6σ violation of the Leggett-Garg inequality and, very recently, to show the Hong-Ou-Mandel interference of indistinguishable atoms in the optical lattice.

I will conclude with an outlook towards experiments exploring topological transport phenomena such as the existence of chiral matter-wave currents spinning in a frictionless way around a topological island.


Seminar, March 8, 2016, 15:00. ICFO’s Seminar Room

Hosted by Prof. Maciej Lewenstein