US-12621136-B2 - Quantum key distribution protocol with weak measurements

US12621136B2US 12621136 B2US12621136 B2US 12621136B2US-12621136-B2

Abstract

A quantum key distribution (QKD) receiver is provided for communicating with a transmitter that produces a plurality of entangled photon qubit pairs to send one qubit from each pair randomly alternating between basis states. The receiver includes a first polarized beam splitter, an orthogonal pair of photon detectors, a weak measurement apparatus, a broadcaster, an error rate estimator, and a post-processor. The first splitter receives the one qubit for passage or reflection. The photon detector pair measures the one qubit from passage or reflection. The apparatus performs a weak measurement on the one qubit and includes an impedance device to induce time delay, a pair of mirrors flanking the impedance device, and second and third polarized beam splitters for alternatively passing the one qubit to each other and to the pair of mirrors. The broadcaster for sending weak measurement results from the detectors to the transmitter. The error rate estimator determines whether the weak measurement satisfies a bit error threshold. The post-processor corrects the weak measurement from one of the basis states in response to a shared random key from the transmitter.

Inventors

Jacob M. Farinholt
James E. Troupe

Assignees

UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF THE NAVY

Dates

Publication Date: 20260505
Application Date: 20200409

Claims (4)

1 . A quantum key distribution (QKD) receiver for communicating with a transmitter that produces a plurality of entangled photon qubit pairs to send one qubit from each pair randomly alternating between basis states, said receiver comprising: a first polarized beam splitter for receiving the one qubit for passage or reflection; an orthogonal pair of photon detectors for measuring the one qubit from said passage or said reflection; an apparatus for performing a weak measurement on the one qubit, including an impedance device to induce time delay, a pair of mirrors flanking said impedance device, second and third polarized beam splitters for alternatively passing the one qubit to each other and to said pair of mirrors, and a pair of lenses flanking said second and third splitters to rotate the one qubit; a broadcaster for sending weak measurement results from said detectors to the transmitter; an error rate estimator to determine whether said weak measurement satisfies a bit error threshold: and a post-processor to correct said weak measurement from one of the basis states in response to a shared random key from the transmitter.
2 . The QKD receiver according to claim 1 , further including a clock in said apparatus for determining time degree of freedom of the one qubit.
3 . The QKD receiver according to claim 1 , wherein said rotate the one qubit by ±π/8.
4 . A communication method for quantum key distribution (QKD) with a transmitter that produces a plurality of entangled photon qubit pairs to send one qubit from each pair randomly alternating between basis states, said method comprising: polarized splitting of the one qubit for passage or reflection via a first polarized beam splitter; detection measuring the one qubit from said passage or said reflection; performing a weak measurement on the one qubit, including inducing time delay, alternatively passing the one qubit between second and third beam splitters and a pair of mirrors, and rotating the one cubit via a pair of lenses flanking said second and third splitters; sending weak measurement results to the transmitter; determining whether said weak measurement satisfies a bit error threshold; and correcting said weak measurement from one of the basis states in response to a shared random key from the transmitter.

Description

CROSS REFERENCE TO RELATED APPLICATION Pursuant to 35 U.S.C. § 119, the benefit of priority from provisional application 62/731,361, with a filing date of Apr. 9, 2019, is claimed for this nonprovisional application. STATEMENT OF GOVERNMENT INTEREST The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. BACKGROUND The invention relates generally to Quantum Key Distribution (QKD) Protocol. In particular, the invention employs weak measurements to provide the QKD Protocol. Communication by signal exchange can be remotely conducted between two parties, Alice and Bob. The signals can constitute a string of characters from an established set to transmit a message from Alice to Bob, for example, or vice versa. Eve, an eavesdropper, seeks to intercept the message with the assistance of her agent Fred to possibly benefit an adversary Charlie, while Alice and Bob prefer to secure their confidences that maintain the privacy of their message. SUMMARY Conventional quantum key distribution (QKD) communication devices yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, various exemplary embodiments provide a QKD receiver for communicating with a transmitter that produces a plurality of entangled photon qubit pairs to send one qubit from each pair randomly alternating between basis states. The receiver includes a first polarized beam splitter, an orthogonal pair of photon detectors, a weak measurement apparatus, a broadcaster, an error rate estimator, and a post-processor. The first splitter receives the one qubit for passage or reflection. The photon detector pair measures the one qubit from passage or reflection. The apparatus performs a weak measurement on the one qubit and includes an impedance device to induce time delay, a pair of mirrors flanking the impedance device, and second and third polarized beam splitters for alternatively passing the one qubit to each other and to the pair of mirrors. The broadcaster for sending weak measurement results from the detectors to the transmitter. The error rate estimator determines whether the weak measurement satisfies a bit error threshold. The post-processor corrects the weak measurement from one of the basis states in response to a shared random key from the transmitter. BRIEF DESCRIPTION OF THE DRAWINGS These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which: FIG. 1 is a diagram view of a basis communication channel; FIG. 2 is a diagram view of an interrupted communication channel; FIG. 3 is a diagram view of weak measurement communication channel; FIG. 4 is a tabular view of a weak measurement procedure; FIG. 5 is a graphical view of a set of observables; FIG. 6 is a graphical view of key rates variation with coupling strength; FIG. 7 is a graphical view of angular shifts in observables; FIG. 8 is a graphical view of uncertainty bias in observables; FIG. 9 is a graphical view of key rates variation with bias angle; FIG. 10 is a diagram view of a communication with measurements; FIG. 11 is a diagram view of an exemplary communication protocol; FIG. 12 is a graphical view of key rates variation with distance; FIG. 13 is a graphical view of key rates variation with distance; and FIG. 14 is a graphical view of key rates variation with distance. DETAILED DESCRIPTION In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. In accordance with a presently preferred embodiment of the present invention, the components, process steps, and/or data structures may be implemented using various types of operating systems, computing platforms, computer programs, and/or general purpose machines. In addition, artisans of ordinary skill will readily recognize that devices of a less general purpose nature, such as hardwired devices, may also be used without departing from the scope and spirit of the inventi