Phase Qubit Decoherence via Zero RF Current Coupling
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Solution Overview
Problem
Phase quantum bits face decoherence issues due to coupling with control and readout circuits, which reduce the quality factor (Q) of the resonant circuit and introduce noise, despite techniques to address dielectric loss in Josephson junctions.
Innovation Solution
A phase quantum bit design incorporating a distributed element, such as a transmission line resonator, coupled to a Josephson junction, where the control and readout circuits are positioned at a location with zero RF current magnitude, minimizing loading and noise coupling, and a shunting impedance is used to enhance tunability and quality factor (Q).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If control and readout circuits are coupled to the resonant circuit, then the quantum bit can be controlled and read, but the quality factor (Q) is reduced and decoherence increases
Solution Approach 1:
A coupled resonant circuit is introduced as an intermediary between the control/readout circuits and the quantum bit resonant circuit. This mediator allows control and readout functions to be performed while isolating the quantum bit from direct loading and noise coupling, thereby maintaining high quality factor and coherence time.
Solution Approach 2:
The system is divided into separate functional modules: the quantum bit resonant circuit, the control circuit, the readout circuit, and the coupled resonant circuit. This segmentation allows each component to perform its function independently while minimizing harmful interactions, particularly by placing coupling points at locations where RF current magnitude is approximately zero.
2Ease of operation
If control and readout circuits are coupled to the resonant circuit, then control and readout functions are enabled, but noise from these circuits couples directly to the resonant circuit
Solution Approach 1:
The coupled resonant circuit serves as a noise-isolating intermediary, preventing direct noise coupling from control and readout circuits to the quantum bit resonant circuit. By positioning coupling points at zero RF current locations, noise interference is minimized while maintaining functional connectivity.
3Ease of operation
If control and readout circuits are coupled to the resonant circuit, then the quantum bit can be accessed, but the circuit is loaded and quality factor (Q) is reduced
Solution Approach 1:
The coupled resonant circuit acts as an energy-isolating intermediary, allowing control and readout operations without directly loading the quantum bit resonant circuit. This maintains the high quality factor by preventing energy dissipation through the control and readout circuits.
Solution Approach 2:
The coupling points are strategically positioned at locations where the RF current magnitude is approximately zero. This local optimization ensures that control and readout circuits can access the quantum bit without introducing significant loading effects at critical points in the resonant circuit.
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 configuration reduces susceptibility to noise from control and readout circuitry, maintaining a high quality factor (Q) and coherence time, while minimizing decoherence effects.
Implementation Method 1
The phase quantum bit comprises: a Josephson junction and a distributed element coupled to the Josephson junction
Implementation Method 2
The coherence time of the quantum bit is determined in part by the quality factor (Q) of the resonant circuit
Data Source
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AI summary
A phase quantum bit is disclosed. In one embodiment, the phase quantum bit may comprise a Josephson junction and a distributed element coupled to the Josephson junction. The distributed element provides a capacitive component and an inductive component of the phase quantum bit.