rf SQUID Qubit Coupler for Tunable Transverse and ZZ Coupling
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Solution Overview
Problem
Current quantum computing approaches, particularly the circuit model, face challenges in maintaining qubit coherence for extended periods, limiting the practical implementation of quantum computers, and existing methods for solving computational problems beyond classical computing capabilities are inefficient due to the limitations of digital computers.
Innovation Solution
The development of controllable qubit coupling systems using rf SQUIDs with compound Josephson junctions and magnetic flux inductors allows for adjustable coupling between qubits, enabling anti-ferromagnetic, ferromagnetic, transverse, and zero couplings, which can extend qubit coherence and facilitate more efficient quantum computations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If qubits are coupled using traditional methods, then basic coupling functionality is achieved, but the ability to achieve multiple coupling states (anti-ferromagnetic, ferromagnetic, transverse, zero coupling) is limited
Solution Approach 1:
The patent implements dynamic control of coupling states by making the coupler's magnetic properties adjustable through external magnetic flux applied to the SQUID loop. This allows the system to transition between different coupling states (anti-ferromagnetic, ferromagnetic, transverse, zero coupling) on demand, resolving the contradiction between coupling versatility and system complexity by using a single dynamically controllable component rather than multiple fixed couplers
Solution Approach 2:
The patent changes the magnetic coupling parameter (βL) of the SQUID coupler by adjusting the applied magnetic flux to control the coupling state between qubits. By varying this parameter, the system can achieve different coupling regimes including transverse coupling for quantum annealing and ZZ coupling for circuit model computation, thereby achieving multiple coupling functionalities through parameter adjustment rather than structural complexity
2Duration of action of moving object
If qubit coherence time is extended for circuit model quantum computation, then quantum error correction becomes possible, but the coherence time requirement becomes 1,000 times the single-gate time which is currently unachievable
Solution Approach 1:
The patent introduces a SQUID-based coupler as an intermediary component between qubits, which mediates the interaction and allows for controlled coupling while isolating the qubits from each other when not needed. This intermediary approach enables quantum annealing computation that does not require the extremely long coherence times needed for circuit model quantum error correction, thereby resolving the contradiction between coherence time duration and error correction reliability
Solution Approach 2:
The patent replaces the circuit model gate-based mechanical operation with quantum annealing that utilizes the natural physical evolution of coupled quantum systems. This substitution eliminates the need for repeated gate operations that accumulate errors over time, allowing computation to proceed with shorter coherence times while maintaining reliability through the inherent robustness of quantum annealing
3Productivity
If transverse coupling is implemented using rf SQUID with βL > 1, then quantum annealing computation efficiency is improved, but the control precision of coupling coefficients becomes more challenging
Solution Approach 1:
The patent implements feedback control mechanisms to monitor and adjust the magnetic flux applied to the SQUID coupler, ensuring precise control of the coupling coefficient. By measuring the actual coupling state and adjusting the control parameters accordingly, the system achieves both the desired transverse coupling for quantum annealing efficiency and the necessary precision in coupling coefficient control
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 enhances qubit coherence and enables more efficient quantum computations by allowing for controlled coupling states, improving the ability to solve complex problems like QMA-complete and optimization problems, and reducing computational time by changing quantum phase transitions.
Implementation Method 1
an rf SQUID having a loop of superconducting material interrupted by a compound Josephson junction
Implementation Method 2
a first magnetic flux inductor coupled to the compound Josephson junction and capable of controlling a βL parameter of the coupling system
Implementation Method 3
a loop of superconducting material interrupted by a compound Josephson junction
Implementation Method 4
adjusting a first amount of flux, produced by the first magnetic flux inductor, threading the compound Josephson junction
Data Source
AI summary
A coupling system may include first and second magnetic flux inductors communicatively coupled to a Josephson junction of an rf SQUID. The coupling system may allow transverse coupling between qubits. A superconducting processor may include at least one of the coupling systems and two or more qubits. A method may include providing first, second and third coupling structure to control the coupling system.