researchers at the massachusetts institute of technology (mit) in cambridge have demonstrated a new technique for causing photon-photon interactions at room temperature (rather than at very low temperatures, as is the standard practice) using a silicon crystal with distinctive patterns etched in it.

a micrograph of the mit researchers’ new device, with a visualization of electrical-energy measurements
and a schematic of the device layout superimposed on it. (massachusetts institute of technology)

the crystal causes nonlinearities in the transmission of an optical signal, according to a report on the mit website.

the article explained, “quantum computers harness a strange physical property called ‘superposition,’ in which a quantum particle can be said to inhabit two contradictory states at the same time. the spin, or magnetic orientation, of an electron, for instance, could be both up and down at the same time; the polarization of a photon could be both vertical and horizontal.”

it added, “because photons aren’t very susceptible to interactions with the environment, they’re great at maintaining superposition; but for the same reason, they’re difficult to control. and quantum computing depends on the ability to send control signals to the qubits.”

the device that the mit researchers created consists of a long, narrow, silicon crystal with holes etched in it. the holes narrow as they approach the center, with the two smallest holes separated by another narrow channel with two sharp concentric tips.  the holes trap light and the tips concentrate the light’s electric field.

a dielectric material is added between the tips that creates an electron wobble as a photon’s electric field passes, which is exaggerated by the tips that concentrate the electrical fields of the photons.

the device allows a single photo to pass through undisturbed, but if two photons in the right quantum states enter then they are reflected back. the device can be tuned to specific frequencies and to specific quantum states, which means that one photon’s quantum properties could impact how a second photon is handled.

“the quantum state of one of the photons can thus be thought of as controlling the quantum state of the other,” the article said. “and quantum information theory has established that simple quantum ‘gates’ of this type are all that is necessary to build a universal quantum computer.

while there is plenty of research left to do before this can be used to create a working quantum computer, researchers are confident that they have made another step forward in the interaction of light particles.

the research was recently published in physical review letters. the abstract stated:

“we propose a photonic crystal nanocavity design with self-similar electromagnetic boundary conditions, achieving ultrasmall mode volume (veff). the electric energy density of a cavity mode can be maximized in the air or dielectric region, depending on the choice of boundary conditions.

“we illustrate the design concept with a silicon-air one-dimensional photon crystal cavity that reaches an ultrasmall mode volume of veff∼7.01×10−5λ3 at λ∼1550  nm. we show that the extreme light concentration in our design can enable ultrastrong kerr nonlinearities, even at the single-photon level.

“these features open new directions in cavity quantum electrodynamics, spectroscopy, and quantum nonlinear optics.”