title: Gaussian private quantum channel with squeezed coherent states.
abstract: While the objective of conventional quantum key distribution (QKD) is to secretly generate and share the classical bits concealed in the form of maximally mixed quantum states, that of private quantum channel (PQC) is to secretly transmit individual quantum states concealed in the form of maximally mixed states using shared one-time pad and it is called Gaussian private quantum channel (GPQC) when the scheme is in the regime of continuous variables. We propose a GPQC enhanced with squeezed coherent states (GPQCwSC), which is a generalization of GPQC with coherent states only (GPQCo) [Phys. Rev. A 72, 042313 (2005)]. We show that GPQCwSC beats the GPQCo for the upper bound on accessible information. As a subsidiary example, it is shown that the squeezed states take an advantage over the coherent states against a beam splitting attack in a continuous variable QKD. It is also shown that a squeezing operation can be approximated as a superposition of two different displacement operations in the small squeezing regime.
authors.affiliation: School of Computational Sciences, Korea Institute for Advanced Study, Hoegiro 85, Dongdaemun, Seoul 130-722, Korea.
authors.forename: Kabgyun
authors.initials: K
authors.lastname: Jeong
authors.affiliation: School of Computational Sciences, Korea Institute for Advanced Study, Hoegiro 85, Dongdaemun, Seoul 130-722, Korea.
authors.forename: Jaewan
authors.initials: J
authors.lastname: Kim
authors.affiliation: Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543, Singapore.
authors.forename: Su-Yong
authors.initials: SY
authors.lastname: Lee