A Tolerance‐Enhanced Spontaneous Parametric Downconversion Source of Bright Entangled Photons

Abstract

Spontaneous parametric down‐conversion (SPDC), a primary resource of photonic quantum entangled states, strongly depends on the intrinsic phase matching condition. This makes it susceptible to changes in factors such as the pump wavelength, crystal temperature, and crystal axes orientation. Such intolerance to changing environmental factors prohibits deployment of SPDC‐based sources in non‐ideal environments outside controlled laboratories. Here, a novel system architecture based on a hybrid linear and non‐linear solution that is shown to make the source tolerance‐enhanced without sacrificing brightness. This linear solution is a lens‐axicon pair, judiciously placed, which is tested together with two common non‐linear crystals, quasi‐phase‐matched periodically‐poled KTiOPO4, and birefringent‐phase‐matched BiB3O6. This approach has the benefit of simultaneous tolerance to the environment and high brightness, which is demonstrated by using the proposed architecture as a stable entangled photon source and a spectral brightness as high as 22.58 ± 0.15 kHz mW−1 with a state fidelity of 0.95 ±3.33333pt0.02$\pm \nobreakspace 0.02$, yet requiring a crystal temperature stability of only ±0.8 °C, a 5 × enhanced tolerance as compared to the conventional high brightness SPDC configurations is reported. This solution offers a new approach to deployable high‐brightness quantum sources that are robust to their environment, for instance, in satellite‐based quantum applications.

Design and implementation of a tunable crystal-heater for spectral variation of entangled non-degenerate photon pairs generated by spontaneous parametric down-conversion

“…The intensity and consequently the spectrum of the SPDC-wavelengths can be determined via the dependence of the deviation from the perfect QPM condition with the wave vector mismatch 𝛥𝑘 and the length L of the NLC according to equation ( 4) and (5) 10,15,18,19 .…”

Near‐Video Frame Rate Quantum Sensing Using Hong–Ou–Mandel Interferometry

“…In the current experiment, we used high brightness single photon source based on PPKTP crystal. [31,32] As a result, we can keep the integration time as low as a few tens of milliseconds. Here, we have also tested the HOM interferometer to measure the vibration frequency of the PEA.…”

“…Recently, we reported a CW pumped high brightness, degenerate single‐photon source at 810 nm using periodically‐poled potassium titanyl phosphate (PPKTP) crystal in non‐collinear, type‐0, phase‐matched geometry. [ 31,32 ] Using the same phase‐matching geometry, here, we report on the experimental demonstration showing the dependence of spectral bandwidth of degenerate SPDC photons and subsequent change in the HOM interference dip width on the length of the PPKTP crystal. Pumping the PPKTP crystal of length 1 mm, using a single‐frequency, CW diode laser at 405.4 nm, we observed the spectral width of the SPDC photons to be as high as 163.42 ± 1.68 nm producing a HOM interference dip having a full‐width‐at‐half‐maximum (FWHM) as small as 4.01 ± 0.04 $$\umu$$m.…”

Near-video frame rate quantum sensing using Hong-Ou-Mandel interferometry

“…Again the required integration time is highly influenced by the brightness of the single-photon source. In the current experiment, we used high brightness single photon source based on PPKTP crystal [31,32]. As a result, we can keep the integration time as low as a few tens of milliseconds.…”

“…Recently, we reported a CW pumped high brightness, degenerate single-photon source at 810 nm using periodically-poled potassium titanyl phosphate (PPKTP) crystal in non-collinear, type-0, phase-matched geometry [31,32]. Using the same phase-matching geometry, here, we report on the experimental demonstration showing the dependence of spectral bandwidth of degenerate SPDC photons and subsequent change in the HOM interference dip width on the length of the PPKTP crystal.…”