Advanced Laser Technology for Quantum Communications (Tutorial Review)

Abstract

Quantum communications is the art of exchanging and manipulating information beyond the capabilities of our conventional technologies using the laws of quantum mechanics. With applications ranging from quantum computing to cryptographic systems with information-theoretic security, there is strong incentive to introduce quantum communications into many areas of our society. However, an important challenge is to develop viable technologies meeting the stringent requirements of low noise and high coherence for quantum state encoding, of high bit rate and low power for the integration with classical communication networks and of scalable and low-cost production for a practical wide-deployment. This tutorial presents recent advances in laser modulation technologies that have enabled the development of efficient and versatile light sources for quantum communications, with a particular focus on quantum key distribution (QKD). Such approaches have been successfully used to demonstrate several QKD protocols with state-of-the-art performance. The applications and experimental results are reviewed and interpreted in the light of a complete theoretical background, allowing the reader to model and simulate such sources.

A wavelength tunable optical transmitter for quantum key distribution

“…This could be done by applying a small change in the driving current supplied to the WT laser, which would cause a phase shift. This approach has been shown to work with fixed wavelength sources, 18 and initial tests with WT lasers show promise. A small phase shift was able to be applied to pulses through direct modulation of the laser.…”

A polarization encoder for satellite-to-ground QKD

“…Using 8 GSa/s of available bandwidth allows us to apply short (∼125 ps) electrical signals to each of the lasers and achieve < 100 ps optical pulses by careful tuning of the VCSEL operating bias. 4 In this demonstration the FPGA was programmed with fixed repeating pulse patterns of length 4096 ns, this provided enough statistics to estimate rates for all the photon states required for the protocol.…”

On-chip quantum secure communications

“…with information encoded as a relative phase between an early and late photonic temporal mode. However, the technique we describe can be adapted to more general cases as described in a recent review [7].…”

“…The resulting pulses can be viewed as phase encoded pulses of random global phase as there is no phase relation between any pair of consecutive pulses. We refer to a pulse generated as above as an information pulse, as it contains all the information needed to create a time-bin qubit [6,7].…”