Quantum Secure Direct Communication Using Differential Time Coding
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Solution Overview
Problem
Existing quantum communication systems face challenges in performing secure direct communication, transmitting multiple bits of classical information without information loss, and accounting for dead time in single photon detectors.
Innovation Solution
A method for quantum secure direct communication using differential time coding, where initial time and phase states are used to encode information, with eavesdropping detection and retransmission based on quantum bit error rate, and encoding time states are generated with time shifts and random numbers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the dimension of transmission information is increased to transmit more bits per photon, then the data rate is improved, but the detection efficiency decreases due to dead time of single photon detectors
Solution Approach 1:
The transmission information is segmented into multiple time bins, where each time bin can independently carry quantum information. By dividing the temporal domain into discrete segments, the system can transmit multiple bits per photon without requiring the detector to respond faster than its dead time, thus maintaining detection efficiency while increasing data rate.
Solution Approach 2:
The patent transitions from spatial encoding to temporal encoding by introducing time bins as an additional dimension for information encoding. Instead of using only the presence/absence of photons, the system encodes information in the temporal distribution across multiple time bins, effectively adding a temporal dimension to the transmission scheme.
2Quantity of substance
If multiple time states are used to encode more information, then the information transmission capacity is improved, but the system complexity increases
Solution Approach 1:
The single photon detector is made multi-functional by enabling it to detect photons across multiple time bins sequentially. The same detector hardware performs multiple detection functions at different time intervals, eliminating the need for multiple parallel detectors and reducing overall system complexity while maintaining high information capacity.
Solution Approach 2:
The system employs periodic time binning where detection windows are repeated at regular intervals. This periodic structure allows the detector to cycle through multiple detection states, encoding information in the temporal pattern of photon arrivals without requiring complex non-periodic detection schemes.
3Speed
If the time interval between photons is reduced to increase transmission speed, then the data rate is improved, but information loss occurs due to detector dead time
Solution Approach 1:
The system pre-defines multiple time bins before transmission begins, with each time bin positioned to avoid overlapping with detector dead periods. This preliminary temporal structuring ensures that photons are distributed in a pattern that anticipates and avoids detector unavailability, preventing information loss while maintaining high transmission speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables secure transmission of multiple bits of classical information without loss, improving data rate and minimizing information loss by considering dead time in single photon detectors.
Implementation Method 1
receiving, from a receiving end on a quantum channel, (i) at least one initial time state configured by including a time interval equal to a dead time of a single photon detector of the receiving end
Data Source
AI summary
The present specification provides a quantum secure direct communication (QSDC) method by which a transmitting end transmits a message on the basis of differential time coding, in a quantum communication system. More specifically, the method comprises the steps of: receiving, from a receiving end on a quantum channel, (i) at least one initial time state configured by including a time interval equal to a dead time of a single photon detector of the receiving end and (ii) at least one initial phase state; receiving, from the receiving end on a classical channel, time state location information for selecting a specific initial time state for encoding of information transmitted to the receiving end; selecting the specific initial time state for the encoding, on the basis of the time state location information: generating an encoding time state by encoding the information on the basis of the selected specific initial time state, the encoding time state being generated by applying a time shift on the basis of a value of the information being encoded; and transmitting a message including the encoding time state to the receiving end through the quantum channel, wherein the message is restored on the basis of a time difference between information on the at least one initial time state stored in the receiving end and information on the encoding time state.