Group-velocity symmetry in photonic crystal fibre for ultra-tunable quantum frequency conversion

Abstract

Low-noise frequency conversion of single photons is a critical tool in establishing fibre-based quantum networks. We show that a single photonic crystal fibre can achieve frequency conversion by Bragg-scattering four-wave mixing of source photons from an ultra-broad wavelength range by engineering a symmetric group velocity profile. Furthermore, we discuss how pump tuning can mitigate realistic discrepancies in device fabrication. This enables a single highly adaptable frequency conversion interface to link disparate nodes in a quantum network via the telecoms band.

Ultratunable Quantum Frequency Conversion in Photonic Crystal Fiber

“…We observe the greatest tuning range for λ p = 787 nm, since adjusting λ p introduces a small group velocity mismatch with the signal [36,38]. In principle, the range can also be extended to shorter λ t , however we observe a strong noise signal due to a seeded four-wave mixing process from the pumps when λ q ∼ 920 nm; for even larger shifts we are limited by the OPO tuning range.…”

“…In this work we demonstrate a QFC device, complimen- tary to χ (2) QFC devices, that can span a wide array of use cases in a quantum network, maintaining efficient BS-FWM in a single PCF across an ultrabroad wavelength range. To achieve this, we have fabricated a PCF that has a group velocity profile which remains symmetric about the zero dispersion frequency for over 1 PHz [38]. This gives an ultrabroad phase matching window, meaning that the pump frequency ω p can remain fixed opposite the input signal ω s , while the second pump frequency ω q , can be tuned to determine the target frequency ω t .…”

Translation from a Distinguishable to Indistinguishable Two-Photon State

“…See Supporting Information, Section III, for the measured spectra of the quantum frequency translation. We expect that dispersion engineering of optical fibers is possible to reduce the leakage to the unwanted bands. ,, …”

“…The experimental visibilities (blue squares in Figure a) are lower than the simulation results due to the frequency distinguishability with the photons in the unintended frequency bands. Dispersion engineering of optical fibers could reduce the effect of photon leakage to unintended frequency bands. ,, The red circle in Figure a is the measured net visibility by adding a narrow bandpass filter with a bandwidth of 130 GHz (0.7 nm) centered at 236.45 THz (1267.89 nm) to the path mode of the transferred idler photons. By doing this, we are able to enhance visibility by blocking more noise photons and photons in unintended frequency bands.…”

“…Figure a shows the phase-matching condition for BS-FWM, where the four fields are symmetrically placed around the frequency of a zero group-velocity dispersion ( f ZGVD ) of the nonlinear medium with group-velocity symmetry. , Varying the frequency of pump field 1 changes that of the target photon without losing the phase-matching condition. Notably, in our experimental configuration, as the group-velocity profile of the nonlinear medium is close to the group-velocity symmetry, we expect that the phase matching is satisfied within the experimental range while fixing the frequency of pump field 2.…”