Heralded spectroscopy with a fiber photon-pair source

Abstract

The correlations between photons generated by nonlinear optical processes offer advantages for many quantum technology applications, including spectroscopy, imaging, and metrology. Here, we use spontaneous four-wave mixing in a birefringent single-mode fiber pumped by a tunable pulsed laser as a broadly tunable source of phase-matched non-degenerate photon pairs for spectroscopy. The pairs are tunable such that the idler beam measures the transmittance spectrum of a sample in the near infrared, while the visible signal beam independently reports correlation information. By the time-resolved counting of both signal and idler photons, we use photon-number correlations to remove uncorrelated noise from the probe beam. Here, we have used heralded spectroscopy to measure the absorption spectrum of gallium arsenide near its band edge, despite the idler photon spectrum being dominated by a large background from spontaneous Raman scattering.

Fiber-based biphoton source with ultrabroad frequency tunability

“…Some of their advantages are large nonlinear interaction lengths [11] and easy integrability into optical networks. However, the frequency tuning of these sources re-quires challenging and hard-to-access methods, such as heating or stretching the fiber [12] or tuning the pump wavelength [13]. On top of that, the performance of these sources is often degraded by their intrinsic Raman-scattering noise.…”

The surprising persistence of time-dependent quantum entanglement

“…In an Imperial experiment [28], the nonlinear stages (NL1 and NL2) take place in opposite directions through the same length of fibre.…”

“…ing a χ (2) interaction, but here we use a degenerate-pump four wave mixing (FWM) (see e.g. [28]). A pump field enters the first nonlinear stage (NL1) and generates entangled signal and idler fields; and whilst the signal is diverted to the final beamsplitter, the idler instead interacts with the to-be-imaged object, and then serves as a co-input, with a copy of the original pump field, to the second nonlinear stage (NL2).…”

“…Since self-phase modulation (SPM) terms are not significant in the low-power regime (see e.g. [28], the interaction Hamiltonian we need here is simply…”

“…Material parameters in the simulations are chosen to be compatible with fiber-based photon pair sources based on spontaneous four-wave mixing [28], which use about 100cm of Thorlabs PM780-HP fibre (see Table I). For the simulation, we convert parameters into units based on meters (m), picoseconds (ps), and field excitation amplitudes referenced back to photon numbers per picosecond.…”