Absolute calibration of a variable attenuator using few-photon pulses.

We demonstrate the ability to calibrate a variable optical attenuator directly at the few-photon level using a superconducting Transition Edge Sensor (TES). Because of the inherent linearity of photon-number resolving detection, no external calibrations are required, even for the energy of the laser pulses, which ranged from means of 0.15 to 18 photons per pulse at the detector. To verify this method, calibrations were compared to an independent conventional calibration made at much higher photon fluxes using analog detectors. In all cases, the attenuations estimated by the two methods agree within their uncertainties.Our few-photon measurement determined attenuations using the Poisson-Influenced K-Means Algorithm (PIKA) to extract mean numbers of photons per pulse along with the uncertainties of these means. The robustness of the method is highlighted by the agreement of the two calibrations even in the presence of significant drifts in the optical power over the course of the experiment.Work of the United States Government. Not subject to copyright.

Photon number squeezing in repeated parametric downconversion with ancillary photon-number measurements.

We present a realistic numerical simulation of a source of number-squeezed photon states employing a cavity-based parametric downconversion (PDC) process. A cavity containing the PDC medium is pumped repeatedly. The cavity recycles only one of the PDC output modes, allowing it to be amplified with each subsequent pump pulse. A photon number resolved (PNR) measurement is made on the other PDC output mode following each pump pulse. Once the PNR measurements indicate that the target number of photons has accumulated in the cavity, the pumping is stopped and the resulting photon state is released. The photon number uncertainty in the resulting state is ~3 dB below that of a mean-equivalent coherent state and furthermore the probability of generating the target photon number is similarly increased.

Photon-number-resolved detection of photon-subtracted thermal light.

We examine the photon statistics of photon-subtracted thermal light using photon-number-resolved detection. We demonstrate experimentally that the photon number distribution transforms from a Bose-Einstein distribution to a Poisson distribution as the number of subtracted photons increases. We also show that second- and higher-order photon correlation functions can be directly determined from the photon-number-resolved detection measurements of a single optical beam.

Demonstrating highly symmetric single-mode, single-photon heralding efficiency in spontaneous parametric downconversion.

We demonstrate a symmetric, single-spatial-mode, single-photon heralding efficiency of 84% for a type-II spontaneous parametric downconversion process. High-efficiency, single-spatial mode collection is key to enabling many quantum information processing and quantum metrology applications.

Stability of device responsivity in silicon photodiodes under cryogenic conditions.

Long-term changes in the responsivity of unbiased silicon photodiodes were observed when operating at the temperature of 90 K. The change manifested as a monotonic increase in current output for a fixed optical power input. The current output has been observed to increase by 20% or more relative to room-temperature output. In all trials, the effect was fully reversed upon returning to room temperature. Analysis of spectrally resolved data showed that the effect is due to formation of a contaminant thin film, of as-yet-unknown composition.