Autocompensating measurement-device-independent quantum cryptography in space division multiplexing optical fibers

Abstract

Single photon or biphoton states propagating in optical fibers or in free space are affected by random perturbations and imperfections that disturb the information encoded in such states and accordingly quantum key distribution is prevented. We propose three different systems for autocompensating such random perturbations and imperfections when a measurement-device-independent protocol is used. These systems correspond to different optical fibers intended for space division multiplexing and supporting collinear modes, polarization modes or codirectional modes such as few-mode optical fibers and multicore optical fibers. Accordingly, we propose different Bell-states measurement devices located at Charlie system and present simulations that confirm the importance of autocompensation. Moreover, these types of optical fibers allow the use of several transmission channels, which compensates the reduction of the bit rate due to losses.

Bell-State-Exchange-Parity-Based Protocol for Efficient Autocompensation of Quantum Key Distribution Encoded in Polarization or Spatial Modes

“…Therefore, as an alternative, we propose a Bell-state-exchangeparity-based protocol (BSEP, in short), which allows for easy, passive full compensation in both the polarization subspace and spatial subspaces (collinear and codirectional modes), assuming that polarization is maintained under spatial encoding. Moreover, the BSEP protocol has measurement-device-independent (MDI) characteristics [19,20], in line with previous work in the field [21][22][23]. Dealing with the issue of particular attacks in the BSEP protocol, we will show a simple attack that can be launched against the protocol and how to tackle it.…”

“…In other words, it contains all the advantages of the MDI-QKD protocol. Accordingly, it is fully different from those based on single-photon states [13,14,21] with only two subsystems (Alice/Bob) which are therefore defenseless to attacks on the photodetection subsystem. The physical system implements a protocol with a built-in autocompensation mechanism.…”

“…However, in this case, it is not enough to make light travel back and forth, since the state is generated at Charlie but is detected at Alice and Bob. Therefore a plug and play based on a single round trip as used, for instance, in [14,21], is not valid for the BBM92 QKD protocol. It requires as a minimum a triple trip (forth-back-forth).…”

“…For the case of polarization modes, if the perturbation on the first trip is P (a SU(2) matrix), then when the pulses return, it becomes P R = ZP T Z, where T denotes the transpose and Z is the third Pauli matrix. Note that off-diagonal elements change sign, apart from being interchanged [15,21], as the axis of propagation is modified when back-propagating, that is,…”

Phase modulation polarization encoding module applied to one-to-many QKD network based on wavelength division multiplexing

“…We now theoretically deduce the stability of the module encoding. The forward and reverse operators for SMF1 between PBS2 and PM are given here first [44,45] :…”