Tunable quantum interference in a 3D integrated circuit

Abstract

Integrated photonics promises solutions to questions of stability, complexity, and size in quantum optics. Advances in tunable and non-planar integrated platforms, such as laser-inscribed photonics, continue to bring the realisation of quantum advantages in computation and metrology ever closer, perhaps most easily seen in multi-path interferometry. Here we demonstrate control of two-photon interference in a chip-scale 3D multi-path interferometer, showing a reduced periodicity and enhanced visibility compared to single photon measurements. Observed non-classical visibilities are widely tunable, and explained well by theoretical predictions based on classical measurements. With these predictions we extract Fisher information approaching a theoretical maximum. Our results open a path to quantum enhanced phase measurements.

Ultrafast-laser-inscribed 3D integrated photonics: challenges and emerging applications

“…Non-classical three-photon interfer-ence has been observed in 3D three-waveguide splitters for quantum interferometry and metrology [170,171]. Indeed, a 3D three-path laser written interferometer has been shown to exhibit enhanced phase sensitivity by using nonclassical photons, thus potentially enabling highly sensitive metrology [172].…”

Progress in ultrafast laser processing and future prospects

“…This distinct feature has recently attracted significant interest for application to the fabrication of compact quantum optics and circuits. A 3D multipath interferometer constructed with femtosecond laser-inscribed optical waveguides has demonstrated tunable quantum interference at the chip scale and is thus capable of quantumenhanced phase measurements [91]. Several functional quantum photonic circuits have been built in glass chips, on which quantum information processing such as photonic boson sampling and Anderson localization (i.e., trapping of scattered fields in a disordered material) has been successfully demonstrated [92,93].…”

Hybrid waveguide-bulk multi-path interferometer with switchable amplitude and phase

“…Bulk-optical interferometers and solutions based on separate fibers 10 are, therefore, at a natural disadvantage compared to waveguide interferometers. 11 Moreover, such integrated solutions do not suffer from a reduction in interference contrast due to limited mode alignment at the recombining beam splitter. For many applications, however, it is also desirable to be able to switch and manipulate the interferometer.…”

“…For example, multi-path interferometers with switchable transmission amplitudes are a promising platform for investigations on the foundations of quantum mechanics, [12][13][14][15][16] whereas tunable phases can be used to tailor the output state of the photons. 11 The two requirements of stability and capability for manipulation are often in conflict with each other. For example, amplitude switching can be realised in purely integrated settings via nested phase-tunable interferometers at the expense of requiring a substantial amount of independent phase shifters for multi-path interferometers.…”

“…This is feasible, albeit challenging, in planar silica-on-silicon circuits, 17,18 but well beyond the state of the art in three-dimensional fused silica waveguides. 11,19 A possible trade-off between these goals, in principle, applicable to any platform, is offered by hybrid solutions, in which parts of the interferometer are integrated, but the manipulation is performed in free space. One approach is the external modulation of the excitation profile sent into a multi-core fiber, effectively amounting to external, tunable beam splitters.…”