Multi-Mode Josephson Coupler for Switchable ZZ Qubit Gates
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Solution Overview
Problem
Existing quantum couplers are inefficient, consume excessive power, and have slow activation times, leading to suboptimal performance in managing interactions and coupling between qubits, particularly in detuned frequency scenarios.
Innovation Solution
A multi-mode coupler component utilizing Josephson junctions and resonators, such as the facemon or L4ZZAP coupler, which enables efficient coupling by switching between modes of oscillation based on pulse application, allowing for controlled ZZ gate activation without constant power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitor is used as a coupler between two transmon style qubits, then ZZ coupling can be provided, but the coupling is always on and cannot be selectively activated
Solution Approach 1:
The coupler component transitions from a static capacitor to a dynamic structure using three Josephson junctions that can be selectively activated. The first and second Josephson junctions are controlled by a control signal to switch between active and inactive states, enabling dynamic control of the ZZ coupling between qubits.
Solution Approach 2:
The invention changes the operational parameters of the coupler by using Josephson junctions with specific critical currents and junction ratios. The third Josephson junction has a critical current that is a fraction (1/N) of the first and second junctions, enabling parameter-based control of coupling strength and activation thresholds.
2Speed
If existing coupler designs are used, then qubit coupling can be achieved, but activation time is slow and speed is limited
Solution Approach 1:
The coupler utilizes periodic oscillation modes (first and second modes) that can be selectively excited. By applying control signals at specific frequencies corresponding to these modes, the coupler can be rapidly activated and deactivated, enabling fast gate operations with reduced activation time.
Solution Approach 2:
The coupler is designed with pre-configured oscillation modes and energy states. The first and second Josephson junctions are positioned and dimensioned in advance to create specific coupling modes, allowing rapid transition between states without requiring gradual adjustment during operation.
3Reliability
If existing coupler designs are used, then qubit interactions can be managed, but power consumption is excessive
Solution Approach 1:
Instead of maintaining continuous coupling, the invention uses periodic activation through oscillation modes. The coupler is activated only when needed for specific gate operations, consuming power only during active coupling periods rather than continuously, thereby reducing overall power consumption while maintaining reliable coupling management.
Solution Approach 2:
The invention extracts and separates the coupling function into distinct oscillation modes that can be independently controlled. By using the third Josephson junction with reduced critical current, the system can achieve the necessary coupling strength with lower energy expenditure, removing excess power consumption from the design.
4Reliability
If a capacitor coupler is used between detuned qubits, then ZZ coupling can be facilitated, but the design lacks versatility and adaptability
Solution Approach 1:
The coupler component provides multiple functions through its two oscillation modes. The first mode enables ZZ coupling between detuned qubits, while the second mode provides additional coupling capabilities. This multi-functional design allows the same coupler to serve different quantum gate operations and coupling scenarios, enhancing versatility.
Solution Approach 2:
The invention introduces asymmetry through the third Josephson junction, which has a critical current that is a fraction (1/N) of the first and second junctions. This asymmetric configuration enables the coupler to handle detuned qubits effectively while maintaining the ability to provide both in-phase and out-of-phase coupling modes, increasing adaptability.
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
Enhances coupling efficiency, reduces power usage, and accelerates activation times, providing faster and more reliable quantum gate operations by managing qubit interactions through controlled mode excitation.
Implementation Method 1
the coupler component can comprise a first Josephson junction, a second Josephson junction, and a third Josephson junction associated with the first Josephson junction and the second Josephson junction in a quantum circuit
Implementation Method 2
a resonator that can be associated with the Josephson junction, wherein the Josephson junction can be associated with a first mode of oscillation and the resonator can be associated with a second mode of oscillation
Data Source
AI summary
Techniques and couplers for managing coupling between qubits are presented. A coupler can be between, and connected to, a first qubit and second qubit. The coupler can comprise three Josephson junctions (JJs). The first and second JJs can be symmetrical, which facilitates creation of a first mode of oscillation and second mode of oscillation opposite of the first mode. Third JJ facilitates a division between the first and second modes. An activation status of a ZZ gate between the first and second qubits can be controlled based on excitation status of first mode and a relationship between first mode and second mode, the excitation status being based on whether a pulse is applied to the coupler. When no pulse is applied, ZZ gate is inactive and there is no coupling. When pulse is applied, first mode is in excited state activating ZZ gate, and there is a coupling between qubits.