Kahraman G. Köprülü

Raman-noise-induced quantum limits for χ (3) nondegenerate phase-sensitive amplification and quadrature squeezing

We present a quantum theory of nondegenerate phase-sensitive parametric amplification in a χ(3) nonlinear medium. The nonzero response time of the Kerr (χ(3)) nonlinearity determines the quantum-limited noise figure of χ(3) parametric amplification, as well as the limit on quadrature squeezing. This nonzero response time of the nonlinearity requires coupling of the parametric process to a molecular vibration phonon bath, causing the addition of excess noise through spontaneous Raman scattering. We present analytical expressions for the quantum-limited noise figure of frequency nondegenerate and frequency degenerate χ(3) parametric amplifiers operated as phase-sensitive amplifiers. We also present results for frequency nondegenerate quadrature squeezing. We show that our nondegenerate squeezing theory agrees with the degenerate squeezing theory of Boivin and Shapiro as degeneracy is approached. We have also included the effect of linear loss on the phase-sensitive process.

14 MHz rate photon counting with room temperature InGaAs/InP avalanche photodiodes

Abstract We have developed high speed gated-mode single-photon counters based on InGaAs/InP avalanche photodiodes for use at 1.55 μm wavelength. Operation at room temperature allows afterpulse probability to be below 0.2% for gate rates up to 14 MHz. We obtained optimum noise-equivalent power of 2.2 ×s; 10−15 W Hz−1/2 at 14% quantum efficiency with dark-count probability of 0.2%. We propose a metric (noise-equivalent power divided by gate frequency) for comparing high speed photon counters and show that for this metric our system outperforms previously reported counters at 1.55 μm wavelength. We demonstrate that for gate widths of a nanosecond or below, the differing amplitude distributions of dark versus light counts allow an optimal decision threshold to be set for a given bias voltage.

Quantum imaging of nonlocal spatial correlations induced by orbital angular momentum

Through scanned coincidence counting, we probe the quantum image produced by parametric down-conversion with a pump-beam carrying orbital angular momentum. Nonlocal spatial correlations are manifested through splitting of the coincidence spot into two.

Lossless single-photon shaping via heralding

Using spontaneous optical parametric downconversion, we experimentally demonstrate heralded generation of shaped single photons, whose modes are tailored indirectly by applying amplitude modulation on the pump field that drives the downconversion process. Our experiment opens a door to creating high-quality, mode-shaped single photons at a substantially higher efficiency than is possible with the existing method of direct single-photon shaping.

Quantum analysis of the z-scan technique

A Gaussian-wave theory is developed for the classical and quantum analysis of the z-scan method that is often used to measure third-order nonlinearities. The theory allows us to compute the transmittance in the z scan and the associated regimes of amplitude squeezing. The classical limits of our theory are in perfect agreement with the previous theoretical results. We show that amplitude squeezing of 1.2dB can be obtained using the z scan with a careful selection of the signal power and the aperture size.

Lossless Single Photon Shaping via Heralding

Using spontaneous optical parametric down-conversion, we analyze and experimentally demonstrate heralded generation of shaped single photons, whose modes are losslessly tailored via amplitude modulation on the pump field that drives the down-conversion process.

Quantum imaging of nonlocal spatial correlations in parametric down-conversion induced by the pump-beam profile

We present a quantum imaging method wherein the quantum image obtained through coincidence counting is dependent on the pump-beam profile. Quantum nature of the nonlocal spatial correlations are experimentally verified.

CW theory for optical fiber photon-pair generation

We derive a CW theory for optical-fiber photon-pair sources, including the effect of non-zero response time of the fibers Kerr nonlinearity. We also include the effects of realistic transmission and detection losses. This theory predicts stronger photon-number correlations than seen experimentally with a pulsed pump, showing the need for development of a pulsed pump theory.

Room temperature high speed InGaAs/InP avalanche photodiode single photon counters

We have developed high speed gated-mode single photon counters based on In-GaAs/InP avalanche photodiodes. Room temperature operation allows for afterpulsing below 0.2% up to 14 MHz gate rate. We measure quantum efficiency of 14% with dark count probability of 0.2%.