Generation of ultraviolet entangled photons in a semiconductor

Abstract

Entanglement is one of the key features of quantum information and communications technology. The method that has been used most frequently to generate highly entangled pairs of photons is parametric down-conversion. Short-wavelength entangled photons are desirable for generating further entanglement between three or four photons, but it is difficult to use parametric down-conversion to generate suitably energetic entangled photon pairs. One method that is expected to be applicable for the generation of such photons is resonant hyper-parametric scattering (RHPS): a pair of entangled photons is generated in a semiconductor via an electronically resonant third-order nonlinear optical process. Semiconductor-based sources of entangled photons would also be advantageous for practical quantum technologies, but attempts to generate entangled photons in semiconductors have not yet been successful. Here we report experimental evidence for the generation of ultraviolet entangled photon pairs by means of biexciton resonant RHPS in a single crystal of the semiconductor CuCl. We anticipate that our results will open the way to the generation of entangled photons by current injection, analogous to current-driven single photon sources.

Generation of entangled-photon pairs from biexcitons in CuCl thin films: Nano-to-bulk crossover regime

“…3. Due to the conservation of energy and wavevector, the positions of the two peaks depend on scattering angle, 10,11 and the entangled two photons are emitted symmetrical about the pump beam as shown in the inset. Two additional peaks called MT and ML in scattering spectra originate from the biexciton decay into transverse and longitudinal exciton levels, respectively.…”

“…This second-order nonlinear process creates polarization-correlated entangled-photon pairs in nonlinear optical crystals with a birefringence. On the other hand, Savasta et al 12 suggested and Edamatsu et al 10 experimentally demonstrated that ultraviolet entangledphoton pairs are generated by the biexciton-resonant hy-…”

“…However, in the first experiment, 10 a part of observed pairs has no entanglement, and this noise was subtracted in the estimation of entanglement of the generated pairs. As indicated by Oohata et al, 13 the main contribution of the unentangled pairs is an accidental collapse of two biexcitons, and this problem has been successfully suppressed by using high-repetition and weak-power laser pulses, because the number of unentangled pairs (noise) is increased by I in 4 for increasing the pumping power I in while the number of entangled pairs (signal) is proportional to I in 2 .…”

Quantum diffraction and interference of spatially correlated photon pairs and its Fourier-optical analysis

“…By utilizing HPS, in the future it will be possible to obtain a spatial resolution of 100 nm or below by using ultraviolet laser light. Recently we have successfully generated ultraviolet entangled photons, whose wavelength is approximately 390 nm, via HPS in a semiconductor crystal [26]. This may open the way to quantum imaging with truly high resolution beyond the classical limit.…”

Generation of correlated photon pairs in different frequency ranges

“…Currently, there are a series of experimental techniques available to produce entangled photons such as parametric down conversion [10][11][12], four-wave mixing [13][14][15], electromagnetically induced transparency [16,17] or cavity QED [18,19]. Furthermore, an atomic memory for correlated photon states has been realized experimentally, playing an essential role for quantum communication over long distances [20][21][22]. Recently, a heralded entanglement source of great practical importance has been demonstrated [23,24].…”