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Method and apparatus for free-space quantum key distribution in daylight

Hughes, Richard J.; Buttler, William T.; Lamoreaux, Steve K.; Morgan, George L.; Nordholt, Jane E.; Peterson, C. Glen; Kwiat, Paul G.

Published Jan 23, 2023• 0 citations

Abstract

A quantum cryptography apparatus securely generates a key to be used for secure transmission between a sender and a receiver connected by an atmospheric transmission link. A first laser outputs a timing bright light pulse; other lasers output polarized optical data pulses after having been enabled by a random bit generator. Output optics transmit output light from the lasers that is received by receiving optics. A first beam splitter receives light from the receiving optics, where a received timing bright light pulse is directed to a delay circuit for establishing a timing window for receiving light from the lasers and where an optical data pulse from one of the lasers has a probability of being either transmitted by the beam splitter or reflected by the beam splitter. A first polarizer receives transmitted optical data pulses to output one data bit value and a second polarizer receives reflected optical data pulses to output a second data bit value. A computer receives pulses representing receipt of a timing bright timing pulse and the first and second data bit values, where receipt of the first and second data bit values is indexed by the bright timing pulse.

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A quantum cryptography apparatus securely generates a key to be used for secure transmission between a sender and a receiver connected by an atmospheric transmission link. A first laser outputs a timing bright light pulse; other lasers output polarized optical data pulses after having been enabled by a random bit generator. Output optics transmit output light from the lasers that is received by receiving optics. A first beam splitter receives light from the receiving optics, where a received timing bright light pulse is directed to a delay circuit for establishing a timing window for receiving light from the lasers and where an optical data pulse from one of the lasers has a probability of being either transmitted by the beam splitter or reflected by the beam splitter. A first polarizer receives transmitted optical data pulses to output one data bit value and a second polarizer receives reflected optical data pulses to output a second data bit value. A computer receives pulses representing receipt of a timing bright timing pulse and the first and second data bit values, where receipt of the first and second data bit values is indexed by the bright timing pulse.

Apparatus and method for secure communication between an earth station and spacecraft. A laser outputs single pulses that are split into preceding bright pulses and delayed attenuated pulses, and polarized. A Pockels cell changes the polarization of the polarized delayed attenuated pulses according to a string of random numbers, a first polarization representing a "1," and a second polarization representing a "0." At the receiving station, a beamsplitter randomly directs the preceding bright pulses and the polarized delayed attenuated pulses onto longer and shorter paths, both terminating in a beamsplitter which directs the preceding bright pulses and a first portion of the polarized delayed attenuated pulses to a first detector, and a second portion of the polarized delayed attenuated pulses to a second detector to generate a key for secure communication between the earth station and the spacecraft.

Quantum optical device authentication technologies are described herein. A first device includes an optical transmitter transmits a plurality of pulses to an optical receiver included on a second device. The optical pulses each have one of two non-orthogonal optical states. The optical receiver measures each of the pulses and the second device records a measured value of the optical state of each pulse. Subsequently, the second device transmits the measured values of the optical states of the pulses to the first device. The first device outputs an indication of whether the second device is authenticated based upon the measured values received from the second device and the optical states of the pulses transmitted by the optical transmitter.

A pseudo-quantum system consisting of laser diodes, wave retarders, beamsplitters, and photodetectors was employed to study encryption of data through binary transmission. The Jones vectors for each optical element can be represented in matrix notation and operated on through linear algebra computation. The laser diodes emit polarized photon pulses which can be represented by 2 x 1 matrices which are treated as transmitted bits. Because of the inherent randomness of polarized photons through a beamsplitter any intermediate detection and subsequent transmission of bits by a third party can immediately be detected. In this study, a total error of 25% was calculated for a 20-bit key and 52-bit protocol when the transmitted signal was intercepted in agreement with theory.

Described herein are various technologies pertaining to detecting tampering of a seal based upon quantum optical communication via a communications channel comprising the seal. A plurality of pulses of light encoded with random data are transmitted on the communications channel, whereupon they are received and their data values measured. The measured data values of the pulses are then compared to the known transmitted data to determine a correlation statistic between the transmitted and received data values. Tampering with the seal can be detected based upon identifying that the correlation statistic has dropped below a threshold non-tampered level of correlation between transmitted and received values.

A method of optical cryptography by using soliton as dark-bright conversion control within a modified add/drop optical filter is proposed.In principle, the coincidence (orthogonal) dark-bright soliton pair has shown promising behaviors, especially when they propagate into the π2 phase shifter, i.e. beamsplitter, π2 phase shift between bright and dark solitons is occurred and separated.Such behaviors can be used to form the orthogonal light modes (solitons), which can be useful for application of cryptography, where in this case the long distance cryptography can be easily managed.In this work we have derived and presented a concept of multi-orthogonal solitons generated by using dark-bright soliton pulses within the modified add/drop optical filter, which is known as a PANDA ring resonator.A pair of optical keys is randomly generated and transmitted into the transmission line, where finally the corrected keys between Alice (sender) and Bob (receiver) can be retrieved.By using the dark-bright soliton conversion control, the obtained output of the dynamic states can be used to randomly form the multi-orthogonal soliton pairs, which can be available for computer and communication security applications, especially for long distance link.

Quantum communication transmitters include beacon lasers that transmit a beacon optical signal in a predetermined state of polarization such as one of the states of polarization of a quantum communication basis. Changes in the beacon polarization are detected at a receiver, and a retarder is adjusted so that the states of polarization in a received quantum communication optical signal are matched to basis polarizations. The beacon and QC signals can be at different wavelengths so that the beacon does not interfere with detection and decoding of the QC optical signal.