Numerical assessment and optimization of discrete-variable time-frequency quantum key distribution

Abstract

The discrete-variables (DV) time-frequency (TF) quantum key distribution (QKD) protocol is a BB84-like protocol, which utilizes time and frequency as complementary bases. As orthogonal modulations, pulse position modulation (PPM) and frequency shift keying (FSK) are capable of transmitting several bits per symbol, i.e., per photon. However, unlike traditional binary polarization shift keying, PPM and FSK do not allow perfectly complementary bases. So information is not completely deleted when the wrong-basis filters are applied. Since a general security proof does not yet exist, we numerically assess DV-TF-QKD. We show that the secret key rate increases with a higher number of symbols per basis. Further we identify the optimal pulse relations in the two bases in terms of key rate and resistance against eavesdropping attacks

648 Hilbert-space dimensionality in a biphoton frequency comb: entanglement of formation and Schmidt mode decomposition

“…The dimensionality and information capacity encoded in entanglement scales with both the number of physical qudits in multipartite systems and the dimensionality of each qudit [1][2][3][4][5][6][7][8][9][10][11] . Entanglement between multi-dimensional quantum systems (e.g., the mode structure of two-photon states of light) [12][13][14][15][16][17][18][19][20][21] can be addressed in spatialtemporal energy properties such as orbital angular momentum 22,23 , position-momentum [24][25][26][27][28][29] , polarization 30,31 , energytime [32][33][34] , and time-frequency [35][36][37][38][39][40][41][42][43][44] , and it has applications that include d-dimensional cluster-state quantum computation 11,38,45 and spectral-...…”

Robust spectral phase reconstruction of time-frequency entangled bi-photon states

“…Being an internal degree of freedom, it is suitable for long distance communications, and allows for propagation through long-distance fibres without affecting the quantum state [1]. Applications exploiting time-frequency encoding range from QKD protocols [2][3][4][5], clock synchronization [6], and quantum communications [7], all of which make use of frequenncy correlated two-photon states.…”