Farouk Albalacy

Single- and many-body interference in a generalized Mach-Zehnder interferometer

Single quantum particles demonstrate interference as seen in Young’s double‐slit experiment, while pairs of quantum particles also exhibit interference on a beam splitter, as revealed by the Hong–Ou–Mandel effect. The aim of this PhD project is to understand how single- and many-particle interference collectively shape quantum many-body dynamics. For instance, we investigate the interplay between single‐ and two-particle interference phenomena in a Mach–Zehnder interferometer as in Figure 1.

Figure 1: Mach-Zehnder interferometer consists of two beam splitters (BS1 and BS2), and two mirrors (M1 and M2), mapping input modes |a> and |b> onto output modes |c> and |d>. ϕ is the phase shift between the two arms of the interferometer. Particles injected in modes |a> and |b> have internal states |α> and |β>, respectively.

We compute the output counting statistics when two bosons or two fermions are injected into the interferometer’s two input ports. Single-particle interference is governed by the phase difference between the interferometer arms, whereas the signature of bosonic or fermionic two-particle interference is isolated by tuning the particles’ distinguishability.

Figure 2: Coincidence probability p(1,1) vs. phase shift ϕ, for different values of the overlap between the internal states, X=|< α|β>|², for bosons and fermions.

Figure 2 shows that the interference contrast upon switching on two particle interference is enhanced for bosons, while being suppressed for fermions. The aim is to study this interplay between single- and many-body interference also for more general interferometers involving larger numbers of particles.

[1] Dittel, Christoph, et al. „Wave-particle duality of many-body quantum states.“ Physical Review X 11, 031041 (2021)
[2] Englert, Berthold-Georg, et al. „Wave-particle duality in multi-path interferometers: General concepts and three-path interferometers.“ International Journal of Quantum Information 6, 129 (2008).

Supervisor: Andreas Buchleitner