Horace P. Yuen

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Strengthening a result of Yuen-Kennedy-Lax and Holevo (YKLH), we relax the (redundant) standard conditions for optimality of minimum-error quantum measurements while retaining sufficiency. This result is made robust by giving quantitative bounds on non-optimality when the simplified conditions fail to hold. These conditions serendipitously appeared as an(More)
The fundamental security and efficiency considerations for fresh key generation will be described. It is shown that the attacker’s optimal probability of finding the generated key is an indispensable measure of security and that this probability limits the possibility of privacy amplification and the amount of fresh key that can be generated. A new approach(More)
We demonstrate theoretically and experimentally that secure communication using intermediate-energy (mesoscopic) coherent states is possible. Our scheme is different from previous quantum cryptographic schemes in that a short secret key is explicitly used and in which quantum noise hides both the bit and the key. This encryption scheme allows optical(More)
Quantum-mechanical calculations of the mean-square fluctuation spectra in optical homodyning and heterodyning are made for arbitrary input and local-oscillator quantum states. In addition to the unavoidable quantum fluctuations, it is shown that excess noise from the local oscillator always affects homodyning and, when it is broadband, also heterodyning.(More)
A team of researchers from the Massachusetts Institute of Technology (MIT) and Northwestern University (NU) is developing a system for long-distance, high- delity qubit tele-portation. Such a system will be required if future quantum computers are to be linked together into a quantum Internet. This paper presents recent progress that the MIT/NU team has(More)
Compared with the use of phase-insensitive linear quantum amplifiers of the same gain G, the use of phase-sensitive linear amplifiers on phase coherent classical light sources in an amplifier-attenuator chain reduces the total quantum noise power by a factor of 4, the homodyne noise variance by 2, and the photon number variance by 2-8 and suppresses the(More)