DESC:FIELD OF THE INVENTION
The present disclosure relates generally to the field of quantum key distribution (QKD) systems, specifically to a system and method for synchronizing timestamps in quantum communication.
BACKGROUND
Quantum Key Distribution (QKD) is essential in the field of secure communication because, in the era of quantum communication, there are many security concerns associated with traditional mathematical algorithms. QKD provides the solution to generate the secure key between two parties by exploiting the principles of quantum mechanics. QKD comprises transmitter and receiver units, where the transmitter encodes and modulates the random data and sends it over the quantum channel. The receiver comprises of photon detector to detect the photons and to give the timestamps of those detections. Due to channel propagation delay, line width of LASER a (light amplification by stimulated emission of radiation) source, separate clock sources at both ends (transmitter & receiver), presence of dark counts and jitter in the channel, there will be offset in the received timestamps. To generate a common key at both ends this offset correction in the timestamps is mandatory. Synchronous Digital Hierarchy (SDH) provides the solution which is flexible and efficient to transport different types of telecommunication traffic synchronously with high reliability.
An inherent challenge in QKD systems is the precise synchronization of clocks between the transmitting and receiving stations to accurately measure the time of arrival of quantum bits (qubits). Timestamps are essential for the decoding of qubits into raw keys. However, discrepancies in clock synchronization can lead to errors in timestamping, thereby affecting the integrity of the raw key and the overall security of the communication.
Current methods for addressing the synchronization issue in QKD systems often involve complex and expensive hardware solutions or require extensive post-processing of the key to correct errors, which can significantly reduce the key generation rate and increase the complexity of the QKD system. Moreover, these methods might not be scalable or practical for long-distance QKD implementations, where timing discrepancies can be more pronounced due to the variability in transmission paths and environmental factors. Further, SDH technology is widely used in telecommunications for transferring multiple digital bit streams over optical fiber using Small Form-factor Pluggable (SFP) modules. While SDH provides a high degree of synchronization accuracy over long distances, its application in the precise timing correction necessary for QKD systems has not been fully explored.
A prior art describes a QKD Synchronization Apparatus and Method wherein the method is adapted to determine a phase difference between the service and quantum channels. The general idea of this disclosure relies on the adaptation of a QKD apparatus to permit the quantum channel to transport classic signal in addition to single photon modes. The detector is switching from the quantum mode to the linear mode used for detecting classic light pulses (classical). After the start-up synchronization, the detector is switched back to the quantum mode. This disclosure is applicable to both free space QKD and ground QKD. This disclosure focuses mainly on phase alignment between quantum and service channels.
Another prior art describes a Quantum Communication Synchronization and Alignment Procedure wherein the disclosure relates to a device and a method carrying out a synchronization method, in particular an alignment method for quantum communication. More particularly, the present disclosure relates to a device and a method carrying out an index alignment procedure capable of aligning the indices of a train of quantum states that are transmitted and detected in quantum communication. The disclosure is based on the characteristics of Hamilton-Cyclic sequences which are sequences of quantum channel signals with a specific pattern encoded onto them which is transmitted repeatedly.
Another prior art describes an apparatus and method for QKD quantum communication channel continuous synchronization and alignment wherein the disclosure relates to a method of synchronizing two transmission channels between a transmitter and a receiver, one being a quantum channel, transmitting quantum key signals and the other, a service channel, transmitting information data signals. The two channels are synchronized by means of clock signals transmitted from the transmitter to the receiver. QKD apparatus is going to operate at its operating throughput without any interruptions due to the synchronization procedure.
Another prior art describes a Quantum Key Distribution Method and Apparatus wherein the QKD transmission apparatus comprises a Global Positioning System (GPS) receiver module operable to receive a GPS signal, and a processor operable to use the GPS signal to derive a clock signal for transmission of a QKD signal. The derived clock signal is shifted by the processor by a predetermined time value in order to provide a modified clock signal.
Accordingly, there is a need to address one or more of the above-mentioned disadvantages or other shortcomings or at least mitigate them and provide a useful alternative.
SUMMARY
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the disclosure. This summary is neither intended to identify key or essential inventive concepts of the disclosure nor is it intended for determining the scope of the disclosure.
The present disclosure provides a system for synchronizing timestamps in quantum communication. The system comprises an FPGA receiver, and an FPGA transmitter. The FPGA transmitter comprises a TX module and an SDH host module. The FPGA receiver comprises an RX module and an SDH client module. The RX module in communication with SDH client module is configured to generate a plurality of timestamps based on received plurality of photons by a detector and demodulation module. The RX module in communication with SDH client module is configured to generate a preamble window by a phase alignment module based on the generated plurality of timestamps. The preamble window indicates a predefined pattern sequence. The RX module in communication with SDH client module is configured to construct a histogram based on the generated preamble window. The RX module in communication with SDH client module is configured to compute offset based on identifying the constructed histogram is matching with a predetermined histogram pattern. The RX module in communication with SDH client module is configured to adjust the computed offset in the preamble window to calculate the transmission delay.
The present disclosure provides a method for synchronizing timestamps in quantum communication. The method includes generating plurality of timestamps based on received plurality of photons by a detector and demodulation module. The method further includes generating a preamble window by a phase alignment module based on the generated plurality of timestamps. The preamble window indicates a predefined pattern sequence. The method further includes constructing a histogram based on the generated preamble window. The method further includes computing a first offset based on identifying the constructed histogram is matching with a predetermined histogram pattern. The method further includes computing a transmission delay based on adjusting the computed first offset in the preamble window.
To further clarify the advantages and features of the present subject matter, a more particular description of the disclosed system and a method will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. It is to be appreciated that these drawings depict only typical embodiments of the disclosure and are therefore not to be considered as limiting its scope. The disclosed system and a method will be described and explained with additional specificity and detail with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Features, aspects, and advantages of embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like reference numerals denote like elements, and wherein:
Figure 1A illustrates an environment for synchronizing timestamps in quantum communication, according to an embodiment of the present disclosure
Figure 1B illustrates an architecture of a system for synchronizing the timestamps in quantum communication, according to an embodiment of the present disclosure;
Figure 2A illustrates a flowchart depicting a method for synchronizing the timestamps in quantum communication, according to an exemplary embodiment of the present disclosure; and
Figure 2B illustrates a flowchart depicting a method for synchronizing the timestamps in quantum communication, according to another exemplary embodiment of the present disclosure.
Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present subject matter.
Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present subject matter so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.
DETAILED DESCRIPTION OF DRAWINGS
The following detailed description of example embodiments refers to the accompanying drawings. The present disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the present disclosure or may be acquired from practice of the implementations. Further, one or more features or components of one embodiment may be incorporated into or combined with another embodiment (or one or more features of another embodiment). Additionally, the flowchart and description of operations provided below relate to at least one of the embodiments in the present disclosure. It should be noted that it is possible to make other embodiments that do not exactly match the flowchart and its description. It is understood that in other embodiments one or more operations may be omitted, one or more operations may be added, one or more operations may be performed simultaneously (at least in part).
It will be apparent that systems and methods or both described herein, may be implemented in different forms of hardware, software, or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and/or methods should not limit their implementations. Thus, the operation and behavior of the systems and/or methods are described herein without reference to specific software code. It is to be understood that software and hardware may be designed to implement the systems and/or methods based on the description herein.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the disclosure and are not intended to be restrictive thereof.
Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present subject matter. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this disclosure belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.
It should be noted that the description merely illustrates the principles of the present disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present disclosure. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the disclosure and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof.
Figure 1A illustrates an environment 100 for synchronizing timestamps in quantum communication, according to an embodiment of the present disclosure.
The environment 100 may include a system 100a implemented in a secure communication setup between Data Center A 100b and Data Center B 100c.
The Data Center A 100b may include a QKD-Transmitter (QKD-Tx) 101 and the Data Center B 100c may include a QKD-Receiver (QKD-Rx) 112. In an embodiment of the present disclosure, the QKD-Tx 101 may be configured to generate and transmit quantum states, typically in the form of photons, through the quantum communication channel.
In an embodiment, the QKD-Rx 112 may be configured to generate a plurality of timestamps based on the received plurality of photons by a detector and demodulation module (DDM) 113.
The QKD-Rx 112 may be further configured to generate a preamble window by a phase alignment module based on the generated plurality of timestamps. In an embodiment, the preamble window indicates a predefined pattern sequence.
The QKD-Rx 112 is further configured to construct a histogram based on the generated preamble window and compute offset based on identifying the constructed histogram matches with a predetermined histogram pattern.
The QKD-Rx 112 is further configured to adjust the computed offset in the preamble window to calculate the transmission delay.
In another embodiment, the QKD-Rx 112 is configured to generate a frame window by a phase alignment module based on the generated plurality of timestamps. The frame window indicates a random pattern sequence.
The QKD-Rx 112 is further configured to construct a histogram based on the generated frame window and compute a second offset based on identifying whether the constructed histogram matches a predetermined histogram pattern.
The QKD-Rx 112 is further configured to the transmission delay based on the computed second offset in the frame window.
Figure 1B illustrates an architecture of a system 100a for synchronizing timestamps in quantum communication, according to an embodiment of the present disclosure. The system 100a may be implemented in the environment 100.
The architecture may include the system 100a. The system 100a may further include the Quantum Key Distribution Transmitter (QKD-Tx) 101 and the QKD-Receiver (QKD-Rx) 112. The QKD-Rx 112 may include a Modulated Weak Coherent Source 102, an field programmable gate array (FPGA) transmitter 103, an oscillator clock source 104, and a Wavelength Division Multiplexing (WDM) unit 105. The QKD-Tx 101 in the system 100a (also referred to as QKD system 100a) is responsible for encoding quantum information into photons and sending them over a quantum channel to the QKD-Rx 112. The QKD-Tx 101 may be configured to generate secure quantum keys by using quantum properties like superposition and entanglement. For example, At the Data Center A 100a, the QKD-Tx 101 sends a stream of encoded photons through an optical fiber to the QKD-Rx 112 of the Data Center B 100c, thereby enabling quantum-secure communication.
The QKD-Rx 112 in the QKD system 100a is responsible for detecting photons, measuring their quantum states, and extracting secure keys. The QKD-Rx 112 may be configured to apply timestamp synchronization to compensate for transmission delays. For example, the QKD-Rx 112 is used to decode received quantum states, ensuring a secure key exchange for encrypting inter-data center data transmissions.
The Modulated Weak Coherent Source (MWCS) 102 may further include a weak coherent laser that emits individual photons (particles of light) and is modulated using binary random data received from a Tx module 103a of the FPGA transmitter 103. The MWCS 102 is a laser-based light source used in the QKD system 100a. The MWCS 102 may be configured to emit weak coherent light pulses, where the average photon number per pulse is carefully controlled to ensure secure quantum communication. The modulation process encodes quantum information (such as polarization, phase, or time-bin states) onto the photons before transmission. For example, in any secure communication systems, the MWCS 102 may be configured to generate modulated weak laser pulses carrying quantum-encoded information. These pulses travel through the optical fiber to the receiver, where they are detected and processed to establish a highly secure encryption key for financial transactions.In an embodiment, the present disclosure provides an advanced method and system for timestamp offset correction in Quantum Key Distribution (QKD), based on Synchronous Digital Hierarchy (SDH) technology to enhance the reliability and precision of secure key exchange. The QKD represents a paradigm shift in secure communication, offering a theoretically impregnable mechanism for exchanging encryption keys, thereby ensuring the quantum-safe communication.
The Tx module 103a is configured to transmit random data to the MWCS 102 for encoding purposes through electrical connection 107. In QKD based systems there are typically three main channels i.e. a classical channel, a synchronization (sync) channel, and a quantum channel 106. The quantum channel 106 is used for transmitting quantum states typically in the form of photons between the QKD-Tx 101 and the QKD-Rx 112. Any attempt to eavesdrop or measure the quantum states may disturb the quantum states, and the disturbance may be detected to ensure the security of key exchange. The classical channel is used for transmitting classical information such as sifting, error correction checksums, privacy amplification, and authentication of data between the QKD-Tx 101 and the QKD-Rx 112. Along with the quantum channel 106 and the classical channel, the sync channel is required to ensure that both the quantum and the classical channel are properly aligned with each other. This alignment is essential for effective error correction and quantum key generation securely.
In the present disclosure, an SDH technology serves the dual purpose of transmitting classical data and ensuring frequency synchronization between the QKD-Tx 101 and the QKD-Rx 112. In an embodiment, the QKD-Tx 101 may include a SDH host 103b (also referred to as SDH host module 103b) that is widely used for backbone telecommunication networks due to its ability to provide synchronous and flexible transport of various types of data traffic. In an embodiment, a data path 108 between the Tx module 103a and the SDH host 103b is provided. The data path 108 may be configured to share classical payload information.
In an embodiment of the present disclosure, a frequency alignment technique based on SDH is implemented such that the classical channel and the sync channel are combined over a single wavelength. The frequency alignment technique optimizes the use of optical bandwidth and ensures seamless communication between the QKD transmitter (QKD-Tx 101) and the QKD receiver (QKD-Rx 112). The classical channel is responsible for transmitting non-quantum information, such as key sifting, error correction, and authentication data, while the sync channel ensures precise timing alignment between the sender and receiver.
The system 100a may multiplex both channels onto a single optical wavelength, reducing the need for additional fiber infrastructure and improving network efficiency. The frequency alignment module ensures that the transmitted signals are properly aligned in frequency, minimizing phase drift and timing mismatches that could degrade system performance.
For example, consider the QKD system 100a deployed between two data centers over a fiber optic link. Traditionally, separate wavelengths would be required for the classical and sync channels, leading to increased fiber resource consumption. , In SDH-based frequency alignment technique, both channels may be multiplexed over a single wavelength, ensuring synchronized transmission and reducing latency. This implementation is particularly advantageous in large-scale quantum communication networks, where optimizing wavelength usage is crucial for maintaining scalability and efficiency.
The SDH host 103b may be configured to convert the classical payload information into SDH frames and communicate over the synchronous transport module link (STM-64). The SDH host 103b is a networking device or module responsible for managing and transmitting high-speed synchronized data over an optical fiber network. In Quantum Key Distribution (QKD) systems, the SDH host 103b is used for precise synchronization between the transmitter QKD-Tx 101 and the receiver QKD-Rx 112.
For example, in a telecom-based QKD system, the SDH Host 103b at the transmitter side encodes classical synchronization information into SDH frames and transmits it alongside the quantum signal. The SDH host at the receiver extracts this timing information to correct timestamp offsets and align quantum key processing.
The SDH frames is a structured data unit used in Synchronous Digital Hierarchy (SDH) networks for transmitting synchronized information over an optical fiber link. The SDH frames carry multiple data streams, including classical synchronization signals and payload information, while ensuring accurate timing and synchronization between communicating nodes. In the QKD systems the SDH frames are used to transmit synchronization signals between the QKD-Tx 101 and the QKD-Rx 112.
For example, in applications requiring secure transactions, the SDH frames are used to synchronize timestamps between two data centers. The SDH Host sends SDH frames over the synchronization channel, ensuring that both ends use the same clock reference for secure quantum key exchange.
The SDH network typically operates based on a global position system or atomic clocks to maintain highly accurate timing. In the present disclosure, the oscillator 104 is configured to provide stable and a reliable clock 109 for both the Tx module 103a and the SDH host 103b. Both the quantum channel 106 and a SDH link 110 of the QKD-Tx 101, are operating on different wavelengths which may be configured to transmit using the WDM 105 and carried over a single optical fiber 111 from the QKD Tx 101 to the QKD-Rx 112.
The QKD-Rx 112 may include the DDM 113, an FPGA transmitter 114, and a Wavelength Division Multiplexing (WDM) unit 115.
The DDM 113 in the QKD-Rx 112 is responsible for extracting quantum information from received photons. The DDM 113 includes Single-Photon Detectors (SPDs) to detect weak quantum signals, demodulators to decode the quantum states (such as polarization or phase), and timestamping electronics to record the precise arrival time of each detected photon. For example, in a quantum-secure banking network, the DDM 113 detects incoming quantum states from the QKD-Tx 101 and extracts quantum bits (qubits) to form a secure encryption key.
The FPGA Transmitter 114 is a programmable hardware module that processes and manages quantum key distribution tasks in the receiver. The FPGA transmitter 114 may be configured to execute QKD protocols such as sifting, error correction, and privacy amplification, ensuring the secure generation of quantum keys. The FPGA transmitter 114 also interfaces with classical and synchronization channels for precise transmission timing. In a military QKD system, the FPGA transmitter 114 filters errors and securely transmits the final quantum key to the cryptographic system for encrypting classified communications.
The Wavelength Division Multiplexing (WDM) Unit 115 is an optical networking component that separates and manages multiple wavelengths traveling through a single fiber. In QKD systems, the WDM unit 115 ensures minimal interference between quantum and classical signals by assigning them to different wavelengths. This enables the transmission of multiple signals over a single optical fiber, reducing infrastructure costs. For example, in a telecom-based QKD deployment, the WDM unit 115 may be configured to extract the quantum signal wavelength from an optical fiber carrying both quantum and classical data, ensuring seamless quantum key distribution without interference.
The DDM 113 may include a single photon detectors and associated electronics. The DDM 113 may be configured to receive and measure quantum state particles transmitted by the QKD-Tx 101. The FPGA receiver 114 may include a receiver (Rx) module 114a that plays a crucial role in extracting quantum photon information such as timestamps from DDM 113 through electrical connection 117. Further, the FPGA receiver 114 may include a Synchronous Digital Hierarchy (SDH) client module 114b that may be configured to obtain timing information from incoming signals and generate the clock and pass to the Rx Module 114a through an internal path 119 in the FPGA transmitter 114. The generated clock is used to achieve the frequency synchronization between the QKD-Tx 101 to the QKD Rx 112. The WDM 115 in the QKD-Rx 112 may be configured to receive wavelengths and separates both of them to two different paths i.e. a quantum channel 116 and a SDH link 118 of the QKD-Rx 112. The QKD-Rx may include a data path 120 between the Rx module 114a and the SDH client module114b to share the classical payload information.
In an embodiment of the present disclosure, the Rx module 114a, in communication with the SDH client module 114b, is responsible for processing quantum signals received via the DDM 113. The Rx module 114a may be configured to generate the plurality of timestamps, which record the precise arrival times of detected photons. The plurality of timestamps is crucial for synchronization and accurate quantum key generation in the QKD system 100a.
In the QKD system 100a, the transmitter (QKD-Tx 101) sends photons carrying quantum information through an optical fiber. At the receiver (QKD-Rx 112), the DDM 113 may be configured to capture the incoming photons and extract quantum states. Since photons travel at the speed of light and can experience timing variations due to fiber length, environmental factors, and quantum noise, the Rx module 114a records the exact time each photon is detected.
In an embodiment, to ensure precise key alignment between the sender and receiver, the Rx module 114a, in collaboration with the SDH client module 114b, generates a plurality of timestamps. The SDH client 114b helps in maintaining synchronization between the quantum and classical channels by providing high-precision clock signals. The plurality of timestamps allows the system 100a to correct for timing offsets, ensuring accurate quantum key extraction and minimizing errors in the final cryptographic key.
For example, consider a government cybersecurity agency implementing a QKD-based communication link between headquarters and a remote intelligence outpost. The QKD-Tx 101 at the headquarters sends quantum-encoded photons to the QKD-Rx 112 at the outpost. The DDM 113 at the outpost captures the photons and passes the information to the Rx module 114a, which timestamps each photon detection.
To maintain precise synchronization, the SDH client module114b integrates high-accuracy time references with the timestamps, ensuring that both locations generate identical quantum keys. This process eliminates errors due to fiber delay variations, ensuring a highly secure encryption key for classified communications.
Upon generating the plurality of timestamps, the Rx module 114a in communication with the SDH client module 114b may be configured to generate a preamble window by a phase alignment module based on the generated plurality of timestamps. The preamble window indicates a predefined pattern sequence. The photons carrying quantum information travel through an optical fiber and are detected at the QKD-Rx 112. Due to fiber transmission delays, environmental variations, and quantum noise, the arrival times of photons may not perfectly match the original transmission times. To correct these variations, the Rx module 114a, working with the SDH client module 114b, uses a phase alignment module to generate a preamble window. The preamble window includes a predefined sequence of photon arrival timestamps, which helps in determining the correct phase alignment of the received quantum data. The preamble window enables the system 100a to identify timing offsets and apply synchronization corrections to maintain accuracy.
The SDH client module 114b ensures that the phase alignment process is precise by using high-resolution clock signals, allowing the system to correctly interpret the received quantum states. Such a synchronization is crucial for minimizing Quantum Bit Error Rate (QBER) and ensuring that the generated quantum key is identical at both ends of the communication link.
In an exemplary scenario, consider a financial institution implementing QKD for secure interbank transactions between its headquarters and a regional branch. The QKD-Tx 101 at the headquarters transmits quantum-encoded photons to the QKD-Rx 112 at the branch. The Rx module 114a records the timestamps of detected photons, but due to optical fiber delay fluctuations, precise alignment with the transmitted quantum states is required.
To address this, the phase alignment module generates a preamble window, consisting of a known pattern of photon timestamps. The SDH client module 114b compares this pattern with the expected sequence and adjusts the system’s phase alignment accordingly. This correction ensures that the extracted quantum key at the branch perfectly matches the transmitted key, securing high-value financial transactions from eavesdropping
The Rx module 114a in communication with the SDH client module 114b module may be further configured to construct a histogram based on the generated preamble window. The histogram is a graphical representation of the distribution of numerical data. The histogram may include bars that represent frequency counts of data points falling within specified ranges (bins). In the context of the Quantum Key Distribution (QKD) system 100a, the histogram is used for analyzing timestamp distributions of received quantum signals. The system 100a generates plurality of timestamps from detected the photons, and these timestamps are used to construct the histogram. By comparing the observed histogram with a predefined pattern, the system 100a may determine synchronization offsets and transmission delays.
For example, imagine a QKD system 100a receiving 1000 photons over a certain time frame. The plurality of timestamps of these photons are recorded, and a histogram is created to group them into bins based on arrival time. If the expected histogram pattern aligns with the received histogram, the system 100a is synchronized. However, if there is a shift or distortion, it indicates transmission delays or potential eavesdropping attempts.
Upon constructing the histogram, the Rx module 114a in communication with the SDH client module 114b may be configured to compute offset based on identifying whether the constructed histogram is matching with a predetermined histogram pattern.
The Rx 114a module in communication with the SDH client module 114b may be configured to adjust the computed offset in the preamble window to calculate the transmission delay.
In the QKD system 100a, the Rx module 114a, in coordination with the SDH client module 114b may be configured to adjust the computed offset within the preamble window to accurately determine the transmission delay. The preamble window contains a predefined sequence that serves as a reference for aligning received quantum signals. When the Rx module 114a detects incoming photons, the Rx module 114a is configured to compare actual arrival time with an expected reference timestamp. Any discrepancy between these values results in a computed offset, which is influenced by factors such as fiber optic transmission delays, processing time, and environmental variations. To maintain synchronization, the SDH client module 114b adjusts this offset, ensuring that received signals remain accurately aligned with the transmission timing.
For example, consider the QKD system 100a transmitting quantum states between Data Centre A (QKD-Tx 101) and Data Centre B (QKD-Rx 112) over a 50 km fiber optic link. If the expected arrival time of a photon is T0, but due to transmission delays, the actual arrival time is T1, the system 100a may be configured to compute the offset as T1 - T0. The SDH client module 114b then adjusts this offset, factoring in both optical propagation delay and hardware processing delay. This adjustment is critical for ensuring secure and reliable quantum key exchange, as accurate synchronization minimizes bit errors and helps detect potential eavesdropping attempts, which could introduce timing anomalies.
In another embodiment, the Rx module 114a in communication with the SDH client module 114b may be configured to generate a frame window by a phase alignment module based on the generated plurality of timestamps. The frame window indicates a random pattern sequence.
The Rx module 114a in communication with the SDH client module 114b may be configured to construct the histogram based on the generated frame window.
The Rx module 114a in communication with the SDH client module 114b may be further configured to compute a second offset based on identifying the constructed histogram matching a predetermined histogram pattern.
The Rx module 114a in communication with the SDH client module 114b may be further configured to adjust the transmission delay based on the computed second offset in the frame window.
In an exemplary scenario, consider a real-time quantum communication scenario where two secure data centers, the Data Center A 100b (the QKD-Tx 101) and the Data Center B (the QKD-Rx 112), are connected through the single optical fibre 111 and the classical channel utilizing Synchronous Digital Hierarchy (SDH) technology for precise synchronization.
At Data Center A 100b, weak coherent light pulses carrying quantum bits (qubits) are transmitted through the quantum channel at regular intervals. Due to quantum effects, some of these photons are lost in transit, while others successfully reach the Data Center B 100c, where they are detected by a single-photon detector in the DDM 113. As each photon is detected, the Rx module 114a records the exact time of arrival and generates a plurality of timestamps. These timestamps are critical for aligning the received quantum data with the original transmission time.
Furthermore, the Rx module 114a, in communication with the SDH client module 114b, generates a preamble window using the timestamps. The preamble window consists of a predefined pattern sequence. For example, a Pseudo-Random Binary Sequence (PRBS) that was previously transmitted by the Data Center A 100a. This predefined pattern helps in aligning the received data phase with the transmitted phase, ensuring the quantum key bits are correctly reconstructed.
The Rx module 114a may be configured to construct a histogram based on the detected timestamps within the preamble window. The histogram helps visualize the distribution of photon arrivals and identify any timing discrepancies. The Rx module 114a computes the first offset based on comparing the constructed histogram with a predetermined reference histogram pattern. This offset represents the delay introduced due to fiber optic transmission, clock jitter, and environmental disturbances.
Once the offset is computed, the Rx module 114a adjusts the timestamps accordingly to calculate the transmission delay, ensuring accurate synchronization between the transmitter and receiver.
Upon determining the transmission delay, the Rx module 114a may be configured to generate a frame window, which, unlike the preamble window, consists of a random pattern sequence based on newly received photon timestamps. A second histogram is then constructed using this frame window data, and a second offset is computed by comparing the histogram with a predetermined reference pattern.
If the system 100a detects any drift in timing (due to environmental factors like temperature changes or fiber expansion), the Rx module 114a dynamically adjusts the transmission delay based on the second computed offset. This ensures the system remains synchronized without requiring frequent recalibration.
Figure 2A illustrates a flowchart depicting a method 200 for synchronizing the timestamps in quantum communication, according to an exemplary embodiment of the present disclosure.
At step 202, the method 200 includes generating the plurality of timestamps based on received plurality of photons by the DDM 113.
At step 204, the method 200 may include generating the preamble window by the phase alignment module based on the generated plurality of timestamps. The preamble window indicates the predefined pattern sequence.
At step 206, the method 200 may include constructing the histogram based on the generated preamble window. At step 208, the method 200 may include computing the first offset based on identifying whether the constructed histogram is matching with the predetermined histogram pattern.
At step 210, the method 200 may include computing the transmission delay based on adjusting the computed first offset in the preamble window.
Figure 2B illustrates a flowchart depicting the method 200 for synchronizing timestamps in quantum communication, according to another exemplary embodiment of the present disclosure.
At step 212, the method 200 may include generating the frame window by the phase alignment module based on the generated plurality of timestamps. The frame window indicates random pattern sequence.
At step 214, the method 200 may include constructing the histogram based on the generated frame window.
At step 216, the method 200 may include computing the second offset based on identifying the constructed histogram is matching with the predetermined histogram pattern. At step 218, the method 200 may include adjusting the transmission delay based on the computed second offset in the frame window.
The present disclosure provides various advantages:
The present disclosure provides a precise timestamp synchronization mechanism that enhances the accuracy of Quantum Key Distribution (QKD), ensuring reliable alignment between the transmitter and receiver for secure quantum communication.
The present disclosure provides an enhanced quantum key generation accuracy, reducing bit errors through dynamic transmission delay adjustments, thereby improving the reliability and security of key exchange.
The users may benefit from real-time drift correction, allowing continuous monitoring and adjustment of phase and offset drifts without requiring frequent manual recalibration, ensuring long-term system stability.
The present disclosure provides a scalable solution for long-distance communication, leveraging Synchronous Digital Hierarchy (SDH) technology to enable timestamp synchronization across extensive optical fiber networks for global quantum-secure communications.
The present disclosure provides an optimized approach for high-speed quantum networks, supporting continuous quantum key exchange without interrupting data transmission, making it suitable for high-throughput secure communication systems.
The present disclosure provides adaptability to various QKD protocols, including Coherent One-Way (COW) and Differential Phase Shift (DPS), allowing seamless integration into different quantum communication architectures.
While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.
The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein.
,CLAIMS:
1. A system (100a) for synchronizing timestamps in a quantum communication, the system (100a) comprising:
a field programmable gate array (FPGA) transmitter (103);
an FPGA receiver (114);
the FPGA transmitter (103) comprising:
a transmitter (Tx) module (103a);
a Synchronous Digital Hierarchy (SDH) host module (103b);
the FPGA receiver (114) comprising:
a receiver (Rx) module (114a);
an SDH client module (114b);
the Rx (114a) module in communication with SDH client module (114b) is configured to:
generate a plurality of timestamps based on the received plurality of photons by a detector and demodulation module (DDM) (113);
generate a preamble window by a phase alignment module based on the generated plurality of timestamps, wherein the preamble window indicates a predefined pattern sequence;
construct a histogram based on the generated preamble window
compute offset based on identifying the constructed histogram matches with a predetermined histogram pattern; and
adjust the computed offset in the preamble window to calculate the transmission delay.
2. The system (100a) as claimed in claim 1, wherein the Rx (114a) module in communication with SDH client module (114b) is configured to:
generate a frame window by a phase alignment module based on the generated plurality of timestamps, wherein the frame window indicates a random pattern sequence;
construct a histogram based on the generated frame window;
compute a second offset based on identifying whether the constructed histogram matches a predetermined histogram pattern; and
adjust the transmission delay based on the computed second offset in the frame window.
3. The system (100a) as claimed in claim 1, wherein a frequency alignment technique based on SDH is implemented such that a classical channel and a sync channel are combined over a single wavelength.

4. A method (200) for synchronizing timestamps in a quantum communication, the method (200) comprising:
generating a plurality of timestamps based on receiving a plurality of photons by a detector and demodulation module (DDM) (113);
generating a preamble window by a phase alignment module based on the generated plurality of timestamps, wherein the preamble window indicates a predefined pattern sequence;
constructing a histogram based on the generated preamble window;
computing a first offset based on identifying the constructed histogram matching with a predetermined histogram pattern; and
computing a transmission delay based on adjusting the computed first offset in the preamble window.

5. The method (200) as claimed in claim 4 comprising:
generating a frame window by a phase alignment module based on the generated plurality of timestamps, wherein the frame window indicates a random pattern sequence;
constructing a histogram based on the generated frame window;
computing a second offset based on identifying the constructed histogram matching with a predetermined histogram pattern; and
adjusting the transmission delay based on the computed second offset in the frame window.
6. The method (200) as claimed in claim 5, wherein the method (200) further comprises:
transmitting, by a SDH pointer, the transmission delay to field programmable gate array (FPGA) transmitter (101).