Multi-mode Quantum Memory Entanglement Multiplexing
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Solution Overview
Problem
Current quantum key distribution systems face challenges in transmitting quantum keys over long distances while maintaining high frequency and simultaneously sharing, transmitting, and repeating quantum signals of multiple angular modes, with existing solutions limited to about 100 km and requiring probabilistic generators with low success rates.
Innovation Solution
A system comprising a multi-mode quantum memory with a magneto-optical trap and two Mach-Zehnder interferometers, configured to generate and multiplex polarisation-entangled photon pairs in multiple directions, allowing for extended distance transmission and increased key transmission frequency by converting 2M memory channels into M channels, achieving efficient entanglement distribution and multiplexing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If quantum key distribution is implemented over long distances, then transmission distance is improved, but signal loss increases and key transmission frequency decreases
Solution Approach 1:
The system divides the long transmission distance into multiple segments by introducing quantum repeaters at intermediate locations. Each repeater handles a specific segment and uses entanglement swapping to extend the overall transmission distance while maintaining signal quality and transmission frequency.
Solution Approach 2:
Quantum repeaters act as intermediary devices between the sender and receiver. These repeaters generate and store entangled states locally, then swap entanglement between adjacent segments, enabling long-distance transmission without direct photon transmission across the entire distance, thus overcoming signal loss while maintaining frequency.
2Productivity
If multiple angular modes are multiplexed, then transmission capacity is improved, but system complexity increases
Solution Approach 1:
The system multiplexes multiple angular modes by utilizing the angular dimension of photon emission. Instead of adding separate physical channels, the system encodes multiple signals in different angular directions (modes) from a single quantum memory, effectively using another dimension to increase capacity without proportionally increasing device complexity.
Solution Approach 2:
A single quantum memory system is designed to generate and transmit multiple angular modes simultaneously. The quantum memory serves multiple functions by producing entangled photon pairs in various angular directions, allowing one device to handle multiple transmission channels and increase overall capacity without requiring separate dedicated systems for each mode.
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
The system enables quantum key transmission over approximately 150 km with increased frequency, allowing for the reproduction of 1 ebit every 6 minutes at 550 km, compared to 1 ebit every 2 days in existing solutions, and supports multiplexing of multiple angular modes, equivalent to 500 generators in parallel operation.
Implementation Method 1
a magneto-optical trap (MOT) equipped with magnetic coils for trapping atoms, cooling lasers
Implementation Method 2
generates and emits pairwise entangled photons (A and B) in at least 10 different directions
Implementation Method 3
two Mach-Zehnder interferometers, configured together with a magneto-optical trap for generating entangled states of multiple angular modes
Data Source
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AI summary
An subject of the invention is a system for generating polarisation-entangled photon pairs for repeating a quantum signal over a distance, comprising a multi-mode quantum memory which comprises a magneto-optical trap (MOT) equipped with magnetic coils for retaining atoms, cooling lasers, pumping lasers for additional illumination of the trap, as well as a Write (W) laser and a Read (R) laser, wherein the quantum memory is optically coupled to two Mach-Zehnder interferometers (MZI) aligned in one axis on both sides of the quantum memory, and between the quantum memory and each of the Mach-Zehnder interferometers (MZI) there is an objective, at least one filter and wave plates. Another subject of the invention is a method for generating polarisation-entangled photon pairs in a multi-mode quantum memory for repeating a quantum signal over a distance.