Quantum light sources
Light is our best medium for sending information over long distances—it moves at nature’s speed limit, and doesn’t degrade for hundreds of kilometers. As quantum technologies become more prevalent, and we strive to transmit quantum information, we will require quantum light.
Nonlinear optical processes, such as spontaneous parametric downconversion (SPDC) and spontaneous four wave mixing (SFWM), are an established standard for generating single photons and other important quantum states of light.
Many nonlinear sources utilize periodic poling—the formation of layers with alternating orientations in the material. We aim to use complex poling patterns in nonlinear media, which can offer enormous potential over conventional periodic poling, to design the next generation of quantum light sources.
Periodic poling produces a sinc-shaped phase-matching function. Alternative phase-matching functions, e.g. Gaussian, can be generated by customizing the poling configuration. This can improve the purity of heralded single photons by two orders of magnitude. (PRA 93, 013801)
Thermal states are fundamental states in many areas of physics, ranging from cosmology to condensed matter. In quantum optics, the thermal state of the radiation field is often decomposed into delocalized states of light, yet decompositions of thermal light involving localized pulses would be highly desirable. In many-body physics, the classical description of the canonical ensemble is very different to the quantum one, also motivating the search for new decompositions.
Recently, we learnt that thermal light cannot be understood as a mixture of broadband coherent pulses (PRL 114, 213601
). This result was both surprising and interesting because representations in terms of coherent states associated with a single frequency do exist (the well-known P-representation). Yet no representation can be found in terms of broadband coherent states (representing localized pulses) or their direct products.
We continue our search for representations of thermal light in terms of pulses. We also explore decompositions of thermal equilibrium of massive particles into localized wave packets, because decompositions into localized eigenstates are difficult to connect with the classical picture of localized particles with definite positions and velocities.
In collaboration with Aurelia Chenu (MIT) and John Sipe (UofT).
The classical picture of thermal equilibrium considers localized particles with a range of positions and velocities; in quantum mechanics, thermal equilibrium is decomposed into delocalized energy eigenstates. We seek quantum mechanical representations of thermal equilibrium involving wave packets with a localized coordinate representation and average velocities.