Tunable Qubit Coupler for Suppressing Spurious Interactions
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Solution Overview
Problem
Scaling up superconducting qubit technology to many qubits is challenging due to issues like spurious interactions, spectator-qubit effects, crosstalk, and frequency crowding, which degrade qubit coherence and gate fidelities.
Innovation Solution
The method involves applying off-resonant microwave drives to coupler modes to engineer tunable multiqubit interactions, allowing for the implementation of fast and high-fidelity two-qubit gates while suppressing unwanted couplings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed-frequency qubits with direct coupling are used, then hardware overhead is reduced and qubit coherence is preserved, but frequency collisions and spurious interactions increase
Solution Approach 1:
The patent introduces a coupler as an intermediary element between qubits to mediate their interactions. This coupler enables controlled coupling and decoupling of qubits, allowing two-qubit gates to be implemented while suppressing spurious direct interactions. The coupler acts as a mediator that can be tuned to enable desired interactions while blocking unwanted ones.
2Object-generated harmful factors
If tunable-frequency qubits with tunable couplers are used, then crosstalk and frequency crowding are reduced, but device complexity and calibration requirements increase
Solution Approach 1:
The patent implements dynamic tunability of the coupler frequency using flux control. The coupler's Josephson energy can be adjusted in real-time, allowing the system to adapt its coupling strength and frequency characteristics. This dynamic control enables the system to avoid frequency collisions and reduce crosstalk by tuning the coupler parameters during operation.
3Speed
If stronger two-qubit coupling is implemented, then gate speed is improved, but spurious multiqubit interactions are enhanced
Solution Approach 1:
The patent applies local quality by making the coupling strength spatially and temporally selective. The coupler is designed to provide strong coupling only to the specific pair of qubits intended for interaction, while maintaining weak coupling to other qubits. This localized coupling approach enables fast two-qubit gates without significantly enhancing spurious interactions with neighboring qubits.
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 connectivity, reduces spurious interactions, and improves the overall performance of superconducting quantum processors by allowing independent tuning of qubit and coupler parameters.
Implementation Method 1
a microwave driver for driving the qubit coupler with microwaves according to a driver power and a third driver frequency
Implementation Method 2
a qubit coupler inductively or capacitively coupling the first qubit to the second qubit according to a ZZ interaction strength
Implementation Method 3
a qubit coupler inductively or capacitively coupling the first qubit to the second qubit according to a ZZ interaction strength
Data Source
AI summary
A system and method provide two-qubit gates and quantum computing circuits built therefrom. Pairs of qubits are inductively or capacitively coupled using a coupler that is driven using an off-resonant microwave drive. By controlling the drive, the ZZ interaction between the qubits can be precisely controlled. In particular, the interaction may be selectively reduced or suppressed, thereby isolating the qubits from each other, or the interaction may be increased to provide fast, controlled-Z, two-qubit gates with high fidelity. Moreover, qubits and couplers may be arranged according to their resonant frequencies into unit cells and replicated to arbitrary size, thereby forming a quantum computer.