Atomic-Stabilized Coherent Photons for Long-Distance Quantum Communication
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Solution Overview
Problem
Current methods for measuring Hong-Ou-Mandel (HOM) interference patterns using independent laser light sources face challenges in maintaining stable frequency alignment over long distances, limiting the clarity and reliability of interference patterns essential for quantum communication technologies like MDI-QKD.
Innovation Solution
The method involves generating continuous-wave coherent photons (CWCP) stabilized to the transition of alkali atoms, using spatially separated quantum light sources with frequency control units to ensure precise frequency stability, allowing for long-distance quantum communication without a quantum repeater, by oscillating photon pairs through optical fiber cables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If independent laser light sources are used for HOM interference measurement, then long-distance quantum communication is enabled, but frequency stability deteriorates over time and distance
Solution Approach 1:
The patent introduces an atomic transition frequency as an intermediary reference standard to mediate the frequency relationship between two independent lasers. By locking both lasers to the same atomic transition frequency (e.g., rubidium D2 line), the system establishes a common reference that maintains frequency stability and coherence over long distances without requiring direct laser-to-laser frequency locking.
Solution Approach 2:
The patent changes the frequency parameter of independent lasers by locking them to a fixed atomic transition frequency. This parameter change transforms the lasers from free-running independent sources to atom-stabilized coherent sources, ensuring that their frequencies remain synchronized and their phase relationship remains stable over time and distance, thereby enabling high-visibility HOM interference patterns.
2Measurement precision
If wavelength-tunable lasers are used to match center wavelengths, then HOM interference measurement is enabled, but frequency maintenance reliability deteriorates
Solution Approach 1:
The patent implements feedback control by using atomic absorption spectroscopy to continuously monitor the laser frequency and adjusting the laser cavity length or current to maintain locking to the atomic transition. This feedback mechanism ensures that the laser frequency remains precisely matched to the atomic reference, providing reliable frequency maintenance and enabling clear HOM interference patterns over extended periods.
3Measurement precision
If narrow transmission wavelength bandwidth filters are used, then high-definition HOM interference patterns are achieved, but technical implementation difficulty increases
Solution Approach 1:
The patent uses atomic transitions as an intermediary frequency reference that naturally provides narrow bandwidth without requiring complex filter implementations. The atomic absorption line serves as a built-in frequency selector that defines the narrow transmission bandwidth needed for high-definition HOM interference patterns, eliminating the need for separate narrowband filters and reducing device complexity.
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
This approach enables stable frequency stabilization of CWCPs, ensuring high visibility of HOM interference patterns regardless of distance, thus enabling reliable long-distance quantum communication without the need for quantum repeaters.
Implementation Method 1
generating a photon in a quantum state from a first quantum light source including an alkali atom or an ensemble of alkali atoms therein as a medium; further generating a photon in a quantum state from a second quantum light source spatially separated from the first quantum light source, including the same medium as that of the first quantum light source therein
Implementation Method 2
oscillating a photon pair obtained by coupling the photons generated by the first and second quantum light sources as a continuous wave coherent photon (CWCP) for quantum communication
Implementation Method 3
In order to measure a Hong-Ou-Mandel (HOM) quantum interference phenomenon of photons emitted from independent laser light sources, the photons involved in the interference must be indistinguishable from each other in all possible degrees of freedom such as polarization, frequency, and spatial mode
Data Source
AI summary
A method and a system for generating independent coherent photons frequency-stabilized to transition of atoms for long-distance quantum communication are provided. The method for generating independent coherent photons frequency-stabilized to transition of atoms for long-distance quantum communication according to the present disclosure, includes generating a photon in a quantum state from a first quantum light source including an alkali atom or an ensemble of alkali atoms therein as a medium, further generating a photon in a quantum state from a second quantum light source spatially separated from the first quantum light source, including the same medium as that of the first quantum light source therein, and oscillating a photon pair obtained by coupling the photons generated by the first and second quantum light sources as a continuous wave coherent photon (CWCP) for quantum communication.