Frame synchronization method for QKD systems

• US 20080037790A1
• Filed: 08/14/2006
• Published: 02/14/2008
• Est. Priority Date: 08/14/2006
• Status: Active Grant

• Current Assignee: MagiQ Technologies, Incorporated
• Original Assignee: MagiQ Technologies, Incorporated
• Inventors: Young, Jonathan, Berzanskis, Audrius, Vig, Harry, Kwok, Brandon
• Granted Patent: US 7,539,314 B2
• Time in Patent Office: Days
• US Class Current: 380/278
• CPC Class Codes: H04L 9/0852 Quantum cryptography transmission systems employing electromagnetic waves other than radio waves, e.g. light, infrared H04B10/00; wavelength-division multiplex systems H04J14/02; WDM arrangements H04J14/03
• CPC Class Codes: H04L 9/12 Transmitting and receiving encryption devices synchronised or initially set up in a particular manner

Abstract

Systems and methods for exchanging and processing encoded quantum signals in quantum key distribution (QKD) systems in real time. A stream of quantum signals is sent from Alice to Bob. Alice only encodes sets or “frames” of the streamed quantum signals based on receiving a “ready” message from Bob. This allows for Bob to finish processing the previous frame of data by allowing different bit buffers to fill and then be used for data processing. This approach results in gaps in between frames wherein quantum signals in the stream are sent unencoded and ignored by Bob. However, those quantum signals that are encoded for the given frame are efficiently processed, which on the whole is better than missing encoded quantum signals because Bob is not ready to receive and process them.

Claims

1. A method of processing quantum signals sent between first and second quantum key distribution (QKD) stations Alice and Bob, the method comprising:

a) at Alice, grouping the quantum signals into frames and encoding and sending a first frame of encoded quantum signals to Bob, and passing basis and key bit data for each encoded quantum signal of the first frame to a raw-bits (RB) buffer at Alice as Alice'"'"'s first frame data;

b) at Bob, detecting the encoded quantum signals in the first frame and passing detection and measurement basis data for the first frame to a raw-bits (RB) buffer at Bob as Bob'"'"'s first frame data; and

c) sending a second and subsequent frames of encoded quantum signals from Alice to Bob while parallel processing data at Alice and Bob from previous frames of encoded quantum signals.

2. The method of claim 1, including synchronizing the sending of frames of encoded quantum signals from Alice to Bob by sending synchronization signals from Alice to Bob.

3. The method of claim 1, including:

Alice generating a continuous stream of quantum signals;

sending from Bob to Alice a “

ready”

signal indicating Bob is ready to receive a frame of encoded quantum signals; and

in response to the ready signal, Alice initiating encoding of the quantum signals in the continuous stream of quantum signals so as to generate a frame'"'"'s worth of encoded quantum signals.

4. The method of claim 1, wherein acts a) and b) constitute a data read-out process, and including:

performing a bit sifting process on a block of data from the RB buffers and storing resultant sifted bits in respective sifted-bits (SB) buffers at Alice and Bob; and

performing an error correction process on a block of data from the SB buffers and storing resultant error-corrected bits in error-correction (EC) buffers at Alice and Bob.

5. The method of claim 4, further including:

performing a privacy amplification process on a block of data from the EC buffers and storing privacy amplified bits in corresponding quantum key (QK) buffers or directly passing the bits to some cryptographic applications at Alice and Bob.

6. The method of claim 1, including generating at Alice a stream of quantum signals and allowing some quantum signals not to be included in any frame to allow for data processing delays.

7. The method of claim 1, including performing qubit indexing by assigning a frame number to each frame and a qubit position of each encoded qubit in each frame.

8. A method of managing a real time process of quantum signal transmission in a quantum key distribution (QKD) system having QKD stations Bob and Alice, comprising:

forming a stream of quantum signals at Alice;

encoding frames of quantum signals at Alice and Bob, wherein each frame starts by Bob sending Alice a ready signal indicating that Bob is ready to encode and detect quantum signals;

detecting each encoded quantum signal at Bob;

storing the encoding and/or measurement results in raw-bits (RB) buffers at Alice and Bob; and

parallel processing the RB buffer data by;

i) copying blocks of data from RB buffers to perform sifting to fill respective SB buffers at Alice and Bob in order to free up space in the RB buffers;

ii) copying blocks of data from the SB buffers to perform error correction to fill respective EC buffers at Alice and Bob in order to free up space in the SB buffers;

iii) copying blocks of data from the EC buffers to perform privacy amplification to form final keys at Alice and Bob.

9. The method of claim 8, including making the stream of quantum signals continuous.

10. The method of claim 8, including allowing some quantum signals in the stream of quantum signals to not be included in a frame in order to allow Bob to finish processing a previous frame'"'"'s worth of data.

11. A method of transmitting quantum signals between two QKD stations Alice and Bob in a QKD system, comprising:

transmitting frames of encoded quantum signals from Alice to Bob only when Bob sends a “

ready”

signal to Alice;

during said transmitting, processing data from previous frames in raw-bits (RB) buffers, sifted-bits (SB) buffers, and error-corrected-bits (EC) buffers at Alice and Bob, including copying and processing blocks of bits from each buffer in order to continually free up space in the buffers to prevent or reduce any delays in transmitting frames.

12. The method of claim 11, including forming a quantum key based on transmitting multiple frames.

13. The method of claim 11, including continuously processing and moving bits from the RB buffers to the SB buffers, from the SB buffers to the EC buffers, and from the EC buffers to privacy amplification (PA) buffers while frames are being transmitted from Alice to Bob.