Researchers of the QITE Photonics team from the MPQ laboratory, recently published an article in the Physical Review Journals.
The authors :
- A. RAYMOND
- A. ZECCHETTO
- J. PALOMO
- M. MORASSI
- A. LEMAÎTRE
- F. RAINERI
- M.I. AMANTI
- S. DUCCI
- F. BABOUX
High-dimensional entangled states of light provide novel possibilities for quantum information, from fundamental tests of quantum mechanics to enhanced computation and communication protocols. In this context, the spatial degree of freedom stands out as particularly suited for on-chip integration. Traditional photonic circuits generate and manipulate photons in a step-by-step fashion, using a sequence of discrete optical components. By contrast, nonlinear waveguide systems offer a promising alternative where photons can be generated and interfere in a continuous manner, unveiling novel capabilities within a reduced footprint.
Here we exploit this concept to implement a compact and versatile source of spatially entangled states of light in AlGaAs nonlinear waveguides arrays. A classical pump beam injected into one or several waveguides generates photon pairs at telecom wavelength by spontaneous parametric down-conversion (SPDC), thanks to the strong second-order nonlinearity of the material (Fig. 1). These photon pairs then continuously tunnel from one waveguide to the other during their propagation, implementing random quantum walks. Compared to previous studies, the walkers are here generated directly inside the device, and the generation can take place at any position along the propagation axis. Besides a gain of integration, this configuration allows for a progressive buildup of spatial entanglement, due to the interference between quantum walks initiated at all possible longitudinal positions. We use a multi-pump configuration to engineer the output quantum state and implement various types of spatial correlations, violating a nonclassicality criterion by several tens of standard deviations [1]. Combined with the ability to engineer at will the device geometry, this novel approach opens the way to simulate in a controlled environment physical problems that are otherwise difficult to access in condensed-matter systems, such as the Anderson localization of multiparticle states or the topological protection of entanglement.
© F. Baboux, MPQ, Université Paris Cité
(a) Principle of spatial entanglement engineering by cascaded quantum walks in a nonlinear waveguide array.
(b) SEM image of a fabricated AlGaAs nonlinear waveguide array.
(c) Example of measured spatially correlated state and
(d) anticorrelated state.