For devices used in quantum computing, quantum sensing, quantum measurement, and other related applications, non-classical states of light like single photons and entangled photons are essential components. Traditional chip fabrication is challenging, but it is possible with millions of dollars’ worth of specialised machinery (and men in white bunny suits). Making a quantum chip is considerably more difficult. Non-linear light sources are also required, and it is crucial to make them fabricatable.
“Canonical Resonant Four-Wave-Mixing in Photonic Crystal Cavities: Tuning, Tolerances and Scaling” shows how to build 20 mm non-classical light sources. In addition to the US National Institute of Standards and Technology (NIST) in Maryland, the authors of the report are from all four corners of France. They begin by talking about quantum resonators like the microring and photonic crystal (PhC) cavity that produce non-classical states of light.
The researchers used the “exotic” photonic crystal to create the first optical parametric oscillator (OPO), which operates at room temperature with a continuous wave pump at the microwatt level.
Instead of silicon, Indium Gallium Phosphide (InGaP) is employed. Although it is simple to construct the emission spectrum, the test vehicle was created to run in the telecom spectral region. The ability to achieve successful parametric conversion with relatively little pump power ( 40 W), a crucial aspect of energy conservation, was also proven.
Correlated photons and quadrature-squeezed vacuum, both of which are sources of quantum information, are emitted by the device while it is below and on the verge of crossing a threshold. Over the threshold, the OPO effectively converts the pump’s power into correlated beams of coherent light. The beginning of this publication occurs at this point. It serves as a sort of “Chapter 2” by offering further measurements on the OPO and covering problems like tuning, quality, tolerance and scaling.
The article is a good read and was published in the IEEE Journal of Selected Topics in Quantum Electronics. Classic science fiction: photons from the pump decay, compressed light, whispering gallery modes, degenerate situations. But wait, there’s a story twist: conditions of “gentle” confinement and time-energy entangled photon pairs. Woah.
Photonic integrated circuits for quantum computing have a cute vocabulary that belies their severity. The Commerce Department Lab, NIST, is involved for a reason. The cybersecurity sector is governed by NIST. Bad actors can break any code if they manufacture their quantum chips before we do. According to the authors, the quantum advantage over current digital processors is that, for extremely complex maths, quantum mechanics within a crystal permits non-exponential scaling.
So let’s return to photonic crystal cavities.
The second section of the study delves deeply into the idea of canonical resonant Four-Wave-Mixing (FWM), which refers to FWM occurring in a cavity allowing only three modes to interact (four in the non-degenerate case). The term “canonical” in this context refers to the specifics of a mathematical Hamiltonian matrix transformation.
When structural disturbance is taken into account, they support their decision to use a PhC cavity rather than ring resonators. They demonstrate how to build a resonator that has no more than the specified number of modes. This is significant since additional modes call for a larger resonator capacity. More crucially, each of these modes can be individually regulated, allowing for customization of their frequency spacing and quality factor.
As a result, the parametric processes can be better controlled, resulting in only the required interactions taking place effectively and reducing parasitic effects. Admittedly, it is quite difficult to achieve this level of control effectively.
The authors compare the three geometries of PhC multimode resonators’ properties in Section III. A 200 nm-thin layer of In0.5Ga0.5P with a two-dimensional pattern of holes makes up the photonic crystal.
A thorough statistical examination of a group of novel devices is covered in Section IV. The authors demonstrate how structural disorder causes fluctuations in the same resonator’s modes that are uncorrelated. Here is where a thorough explanation of the tuning mechanism is given. With good agreement on threshold and slope efficiency, the authors compare theory and experiment on parametric oscillation in 11 OPOs in Section V.
