Heonoh Kim

Two-particle interference experiment with frequency-entangled photon pairs

We present experimental observations of a nonclassic and nonlocal interference effect with frequency-entangled photon pairs. We observed two-photon interference in a Hong–Ou–Mandel interferometer by monitoring the coincidence-counting rate as we varied the path-length difference or the relative time delay between two photons. The quantum-mechanical probabilities of joint detection by two detectors that respond to different frequency components exhibit differences that depend not only on the arrangement of the detector pairs but on the spectral filtering. The experimental results provide more understanding of two-photon entanglement and of the interference effects that arise from superposition of indistinguishable probability amplitudes.

The phase-sensitivity of a Mach–Zehnder interferometer for Fock state inputs

Abstract Phase-sensitivity of some different measurement schemes with a Mach–Zehnder interferometer is studied. The input light is considered to be in a photon number state and the detectors are assumed to be ideal with quantum efficiency of unity. Direct calculation of the operators corresponding to the measurement schemes shows that the uncertainty of the phase-shift measurement can be reduced to the Heisenberg limit of 1/ N ( N is the total number of the photons in the input state) with certain measurement schemes.

The Relation between Statistics of Input Photons and Photocounts

The relation between the statistics of photons in input light on a detector and the measured photocounts by the detector is discussed. The averages and variances of the photocounts are compared with the averages and variances of input photons on practical detectors having quantum efficiencies of

The Phase-sensitivity of a Mach-Zehnder Interferometer for Coherent Light

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Experimental demonstration of error-insensitive approximate universal-NOT gates

. This comparison was made for three kinds of inputs which include Fock state light, coherent light, and thermal light. The calculations were carried out based on the combined operator model for a detector having less-than-unit quantum efficiency.

Phase sensitivity of a quantum Mach-Zehnder interferometer for a coherent state input

We have studied the sensitivity of four different phase shift measurement schemes with a Mach-Zehnder interferometer. The input light is considered to be in a coherent state and the detectors are assumed to be ideal with the quantum efficiency of unity. It is shown by direct calculation of the operators corresponding to the measurement schemes that the uncertainty of the phase-shift measurement is limited to the classical one

Two - Photon Interference Experiment in a Mach - Zehnder Interferometer

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Another Quantum Eraser Experiment with Two - photon States of Light

(m is the average number of the photons in the input state) regardless of the phase-shift measurement schemes.

Single-photon Detection at 1.5 ㎛ Telecommunication Wavelengths Using a Frequency up-conversion Detector

We propose and experimentally demonstrate an approximate universal-NOT (UNOT) operation that is robust against operational errors. In our proposal, the UNOT operation is composed of stochastic unitary operations represented by the vertices of regular polyhedrons. The operation is designed to be robust against random operational errors by increasing the number of unitary operations (i.e., reference axes). Remarkably, no increase in the total number of measurements nor additional resources are required to perform the UNOT operation. Our method can be applied in general to reduce operational errors to an arbitrary degree of precision when approximating any antiunitary operation in a stochastic manner.

Hanbury brown-Twiss effect in a two-photon interference experiment

The phase sensitivity of a Mach-Zehnder interferometer utilizing quantum entanglement is analyzed for a coherent state input. The results show that the Heisenberg limit in the measurement of the phase shift is obtainable with a coherent input. Moreover, the scheme turns out to be immune to the imperfect detector efficiencies. This suggests another promising route for implementing sub-shot-noise measurement schemes.