Conditional generation of an arbitrary superposition of coherent states

We present a scheme to conditionally generate an arbitrary superposition of a pair of coherent states from a squeezed vacuum by means of the modified photon subtraction where a coherent state ancilla and two on/off type detectors are used. We show that, even including realistic imperfections of the detectors, our scheme can generate a target state with a high fidelity. The amplitude of the generated states can be amplified by conditional homodyne detections.Comment: 7 pages, 5 figure

Multiphoton discrimination at telecom wavelength with charge integration photon detector

We present a charge integration photon detector (CIPD) that enables the efficient measurement of photon number states at the telecom-fiber wavelengths with a quantum efficiency of 80% and a resolution less than 0.5 electrons at 1 Hz sampling. The CIPD consists of an InGaAs PIN photodiode and a GaAs JFET in a charge integration amplifier, which is cooled to 4.2 K to reduce thermal noise and leakage current. The charge integration amplifier exhibits a low noise level of 470 nV/Hz1/2. The dark count is as low as 500 electrons/hour.Comment: 4 pages, 4 figures, accepted for Applied Physics letter

Large amplitude coherent state superposition generated by a time-separated two-photon subtraction from a continuous wave squeezed vacuum

Theoretical analysis is given for a two-photon subtraction from a continuous wave (CW) squeezed vacuum with finite time separation between two detection events. In the CW photon subtraction process, the generated states are inevitably described by temporal mutimode states. Our approach is based on Schr\"{o}dinger picture which provides mathematically simple forms and an intuitive understanding of its multimode structure. We show that, in our process, the photon subtracted squeezed vacuum is generated in two temporal modes and one of these modes acts as an ancillary mode to make the other one a large amplitude coherent state superposition.Comment: 9 pages, 8 figure

Experimental Determination of the Gain Distribution of an Avalanche Photodiode at Low Gains

A measurement system for determining the gain distributions of avalanche photodiodes (APDs) in a low gain range is presented. The system is based on an ultralow-noise charge--sensitive amplifier and detects the output carriers from an APD. The noise of the charge--sensitive amplifier is as low as 4.2 electrons at a sampling rate of 200 Hz. The gain distribution of a commercial Si APD with low average gains are presented, demonstrating the McIntyre theory in the low gain range.Comment: 3 pages, 4 figure