Tunable Quantum Coupler with Capacitive Cancellation
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Solution Overview
Problem
Existing quantum computing technologies face challenges with coherent rotations and coherent qubit errors, particularly ZZ errors, due to the coupling between adjacent qubits, which limit the performance and speed of quantum gate operations.
Innovation Solution
A tunable coupler and a capacitor device are used to facilitate a quantum gate between qubits, where the capacitor device generates a coupling opposite in sign to the tunable coupler, allowing for control of qubit interactions and elimination of coherent rotations by tuning the resonant frequency to be smaller than that of the qubits, thereby decoupling them and reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tunable coupler is designed to operate at a resonant frequency above that of the qubits, then coherent rotations and ZZ errors are reduced, but the gate speed becomes slow and it becomes difficult to achieve fast gates for a broad range of detuning
Solution Approach 1:
The patent inverts the conventional frequency relationship by designing the tunable coupler to operate at a resonant frequency BELOW the qubit frequencies rather than above them. This parameter change enables strong ZZ coupling for fast gates while maintaining the ability to eliminate coherent rotations through capacitive coupling cancellation, thus resolving the speed-reliability contradiction
Solution Approach 2:
The patent introduces a capacitor device as an intermediary element that provides an additional coupling path between qubits. This capacitor generates a coupling opposite in sign to the tunable coupler, allowing for precise control and cancellation of coherent rotations while maintaining fast gate speeds through the inverted frequency relationship
2Productivity
If adjacent qubits are coupled together to perform quantum gates, then quantum gate operations are enabled, but coherent rotations and ZZ errors occur on spectator qubits resulting in gate errors
Solution Approach 1:
The capacitor device acts as an intermediary that provides a controlled coupling path between qubits. By generating a coupling opposite in sign to the tunable coupler, it enables precise control over interaction strength and allows for the elimination of harmful coherent rotations on spectator qubits while maintaining necessary gate operations
Solution Approach 2:
The patent changes the resonant frequency parameter of the tunable coupler to be below the qubit frequencies, which fundamentally alters the coupling dynamics. This enables strong ZZ coupling for fast gates while the capacitive coupling can be tuned to cancel coherent rotations, thus enabling gate operations with reduced error rates
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 the speed and fidelity of quantum gate operations by reducing coherent qubit errors and improving the performance of quantum processors by effectively canceling out unwanted qubit interactions.
Implementation Method 1
a capacitor device coupled between the first qubit and the second qubit, where the capacitor device generates a coupling that is opposite in sign to a coupling from the tunable coupler
Implementation Method 2
based on a resonant frequency of the tunable coupler being smaller than a resonant frequency of both the first qubit and the second qubit
Data Source
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AI summary
Devices and/or computer-implemented methods to facilitate a quantum gate between qubits using a tunable coupler and a capacitor device are provided. According to an embodiment, a quantum coupler device can comprise a tunable coupler coupled between terminals of a same polarity of a first qubit and a second qubit, the tunable coupler configured to control a first coupling between the first qubit and the second qubit. The quantum coupler device can further comprise a capacitor device coupled to terminals of an opposite polarity of the first qubit and the second qubit, the capacitor device configured to provide a second coupling that is opposite in sign relative to the first coupling.