Alessandro Farsi

Demonstration of temporal cloaking

Recent research has uncovered a remarkable ability to manipulate and control electromagnetic fields to produce effects such as perfect imaging and spatial cloaking. To achieve spatial cloaking, the index of refraction is manipulated to flow light from a probe around an object in such a way that a ‘hole’ in space is created, and the object remains hidden. Alternatively, it may be desirable to cloak the occurrence of an event over a finite time period, and the idea of temporal cloaking has been proposed in which the dispersion of the material is manipulated in time, producing a ‘time hole’ in the probe beam to hide the occurrence of the event from the observer. This approach is based on accelerating the front part of a probe light beam and slowing down its rear part to create a well controlled temporal gap—inside which an event occurs—such that the probe beam is not modified in any way by the event. The probe beam is then restored to its original form by the reverse manipulation of the dispersion. Here we present an experimental demonstration of temporal cloaking in an optical fibre-based system by applying concepts from the space–time duality between diffraction and dispersive broadening. We characterize the performance of our temporal cloak by detecting the spectral modification of a probe beam due to an optical interaction and show that the amplitude of the event (at the picosecond timescale) is reduced by more than an order of magnitude when the cloak is turned on. These results are a significant step towards the development of full spatio-temporal cloaking.

Demonstration of Temporal Cloaking

We present the first experimental demonstration of cloaking an event in the time domain. Our temporal cloaking scheme is based on the time-space duality and novel split time-lenses.

Strong polarization mode coupling in microresonators

We observe strong modal coupling between the TE00 and TM00 modes in Si3N4 ring resonators revealed by avoided crossings of the corresponding resonances. Such couplings result in significant shifts of the resonance frequencies over a wide range around the crossing points. This leads to an effective dispersion that is one order of magnitude larger than the intrinsic dispersion and creates broad windows of anomalous dispersion. We also observe the changes to frequency comb spectra generated in Si3N4 microresonators due to polarization mode and higher-order mode crossings and suggest approaches to avoid these effects. Alternatively, such polarization mode crossings can be used as a tool for dispersion engineering in microresonators.

Tunable frequency combs based on dual microring resonators.

We demonstrate tunable coupling condition of a silicon nitride microresonator frequency comb. Using a dual-coupled resonator geometry and integrated microheaters, we achieve 13.3 dB of extinction tuning and observe 10-fold increase in generated power.

Ramsey Interference with Single Photons

Interferometry using discrete energy levels of nuclear, atomic, or molecular systems is the foundation for a wide range of physical phenomena and enables powerful techniques such as nuclear magnetic resonance, electron spin resonance, Ramsey-based spectroscopy, and laser or maser technology. It also plays a unique role in quantum information processing as qubits may be implemented as energy superposition states of simple quantum systems. Here, we demonstrate quantum interference involving energy states of single quanta of light. In full analogy to the energy levels of atoms or nuclear spins, we implement a Ramsey interferometer with single photons. We experimentally generate energy superposition states of a single photon and manipulate them with unitary transformations to realize arbitrary projective measurements. Our approach opens the path for frequency-encoded photonic qubits in quantum information processing and quantum communication.

Dual-pumped degenerate Kerr oscillator in a silicon nitride microresonator

We demonstrate a degenerate parametric oscillator in a silicon nitride microresonator. We use two frequency-detuned pump waves to perform parametric four-wave mixing and operate in the normal group-velocity dispersion regime to produce signal and idler fields that are frequency degenerate. Our theoretical modeling shows that this regime enables generation of bimodal phase states, analogous to the χ(2)-based degenerate OPO. Our system offers potential for realization of CMOS-chip-based coherent optical computing and an all-optical quantum random number generator.

Monolithic source of tunable narrowband photons for future quantum networks

Using high-Q Si3N4 microresonators, we generate the narrowest bandwidth (40 MHz) photon pairs, yet achieved for a chip-based source. Its high intrinsic stability and broad tunability are highly promising for interfacing to quantum memory networks.

Quantum optics of spontaneous four-wave mixing in a silicon nitride microring resonator

By varying the width of an exciting pump pulse, very efficient generation of photon pairs, ranging from anti-correlated to nearly unentangled, is possible in existing silicon nitride microring resonators.

Low-noise quantum frequency translation of single photons

We demonstrate quantum frequency translation of single photons via four-wave-mixing Bragg scattering using a liquid nitrogen cooled dispersion-shifted fiber. We achieve 80% photon conversion efficiency with less than 0.001 noise photons per 5ns gate.

Spectrally efficient comb source with coupled microresonators

We demonstrate a spectrally efficient parametric comb source for WDM applications using a Si3N4 dual-coupled microring resonator. This geometry allows for operating wavelength flexibility and avoidance of mode crossings for stable comb generation.