Flux Qubit Readout Circuit Without DC-SQUID Voltage Switching
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Solution Overview
Problem
Existing readout systems for superconducting flux qubits in adiabatic quantum computation and quantum annealing dissipate significant energy, leading to thermalization delays that hinder the performance speed of iterative computations.
Innovation Solution
A superconducting readout system that couples a qubit signal to a variable transformer circuit with a DC-SQUID and primary inductor, allowing a time-varying drive current to be routed through both, preventing the DC-SQUID from switching into a voltage state and minimizing energy dissipation, while using latching qubits to mediate coupling and a shift register or multiplexer circuit to route signals efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC-SQUID is used to read out the state of a superconducting flux qubit, then the qubit state can be determined, but the DC-SQUID switches into a voltage state and dissipates significant energy causing thermalization delays
Solution Approach 1:
The patent introduces a variable transformer circuit as an intermediary between the qubit and the DC-SQUID readout system. This transformer couples the qubit signal to the DC-SQUID in a way that allows state determination without forcing the DC-SQUID to switch into its dissipative voltage state, thereby mediating the interaction to avoid energy loss while preserving measurement capability.
Solution Approach 2:
The patent modifies the operating parameters of the DC-SQUID by using a variable transformer to control the flux coupling. By adjusting the transformer's coupling parameter, the system can determine qubit states while keeping the DC-SQUID in its zero-voltage superconducting state, changing the operational regime to avoid energy dissipation.
2Measurement precision
If a DC-SQUID switches into a voltage state for readout, then the qubit state can be detected, but thermalization delays occur that hinder iterative computation speed
Solution Approach 1:
The variable transformer serves as a mediator that enables qubit state detection without requiring the DC-SQUID to undergo the slow thermalization process. By coupling the qubit signal through the transformer's variable inductance, the system achieves fast readout that does not bottleneck the iterative computation speed.
Solution Approach 2:
The system performs preliminary coupling of the qubit signal to the DC-SQUID through the variable transformer before any state determination is needed. This preliminary setup allows the DC-SQUID to remain in its superconducting state while still being sensitive to qubit states, eliminating the need for slow thermalization between iterations.
3Measurement precision
If existing readout systems are used, then qubit states can be determined, but significant energy dissipation heats the qubits and slows down iterative computations
Solution Approach 1:
The variable transformer circuit acts as a thermal buffer and intermediary, coupling the qubit signal to the DC-SQUID readout system without allowing significant energy transfer that would heat the qubits. This mediator enables state determination while maintaining the qubits at their required low operating temperature.
Solution Approach 2:
The patent replaces the direct electromagnetic coupling mechanism with an inductive coupling through the variable transformer. This substitution allows signal transfer for state determination while minimizing the energy and heat transfer that would otherwise occur in a direct coupling system.
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 reduces thermalization delays and enhances the speed of iterative computations by minimizing energy dissipation during readout, allowing for faster and more efficient determination of qubit states without heating the qubits.
Implementation Method 1
a magnetic flux representative of the state of the superconducting flux qubit is coupled to a DC-SQUID
Implementation Method 2
the primary inductor and the secondary inductor are positioned sufficiently proximate one another to inductively couple signals therebetween
Implementation Method 3
at least one Josephson junction; a superconducting loop (i.e., a 'qubit loop') that is interrupted by at least one Josephson junction
Implementation Method 4
a first superconducting flux qubit including a qubit loop formed of a material that is superconducting below a critical temperature
Data Source
AI summary
Systems and methods for reading out the states of superconducting flux qubits may couple magnetic flux representative of a qubit state to a DC-SQUID in a variable transformer circuit. The DC-SQUID is electrically coupled in parallel with a primary inductor such that a time-varying (e.g., AC) drive current is divided between the DC-SQUID and the primary inductor in a ratio that is dependent on the qubit state. The primary inductor is inductively coupled to a secondary inductor to provide a time-varying (e.g., AC) output signal indicative of the qubit state without causing the DC-SQUID to switch into a voltage state. Coupling between the superconducting flux qubit and the DC-SQUID may be mediated by a routing system including a plurality of latching qubits. Multiple superconducting flux qubits may be coupled to the same routing system so that a single variable transformer circuit may be used to measure the states of multiple qubits.