arXiv subjects

D. Sych

Publications and source records attributed to D. Sych.

5 recordsLinked to original sources

arXiv2023

Applicability of QKD: TerraQuantum view on the NSA's scepticism

Quantum communication offers unique features that have no classical analog, in particular, it enables provably secure quantum key distribution (QKD). Despite the benefits of quantum communication are well understood within the scientific community, the practical implementations sometimes meet with scepticism or even resistance. In a recent publication [1], NSA claims that QKD is inferior to "quantum-resistant" cryptography and does not recommend it for use. Here we show that such a sceptical approach to evaluation of quantum security is not well justified. We hope that our arguments will be helpful to clarify the issue.

quant-ph↗

arXiv2022

Explicit attacks on BB84 with distinguishable photons

Distinguishability of photons in non-operational degrees of freedom compromises unconditional security of quantum key distribution since an eavesdropper can improve attack strategies by exploiting this distinguishability. However, the optimal eavesdropping strategies in the presence of light source side channels are not known. Here we provide several explicit attack strategies on the BB84 protocol with partially distinguishable photons. In particular, we consider the phase-covariant cloning attack, which is optimal in the absence of side channels, and show that there are even better strategies in the presence of side channels. The improved strategies exploit a measurement of the side channel state followed by an attack on the signal photon. Our results explicitly demonstrate reduction of the critical error rate, and set an upper bound on the practical secret key rate.

quant-ph↗

arXiv2012

Informational completeness of continuous-variable measurements

We justify that homodyne tomography turns out to be informationally complete when the number of independent quadrature measurements is equal to the dimension of the density matrix in the Fock representation. Using this as our thread, we examine the completeness of other schemes, when continuous-variable observations are truncated to discrete finite-dimensional subspaces.

quant-ph↗

arXiv2009

Feasibility of free space quantum key distribution with coherent polarization states

We demonstrate for the first time the feasibility of free space quantum key distribution with continuous variables under real atmospheric conditions. More specifically, we transmit coherent polarization states over a 100m free space channel on the roof of our institute's building. In our scheme, signal and local oscillator are combined in a single spatial mode which auto-compensates atmospheric fluctuations and results in an excellent interference. Furthermore, the local oscillator acts as spatial and spectral filter thus allowing unrestrained daylight operation.

quant-ph↗

arXiv2009

Mutually unbiased bases and generalized Bell states

We employ a straightforward relation between mutually unbiased and Bell bases to extend the latter in terms of a direct construction for the former. We analyze in detail the properties of these new generalized Bell states, showing that they constitute an appropriate tool for testing entanglement in bipartite multiqudit systems.

quant-ph↗