Persistent Current Switch With Folded Titanium Geometry
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Solution Overview
Problem
Existing thin film superconducting persistent current switches dissipate excessive power, leading to heating issues in refrigerators and qubits, and have high inductance values that couple noise currents from room temperature electronics, making it difficult to set control currents accurately.
Innovation Solution
The design employs a titanium switch element with a lower superconducting temperature than the connection material, minimizing power requirements and inductance through a folded geometry, and uses a gold-palladium heater with balanced current wiring to reduce noise coupling, allowing precise control of the switch's superconducting state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a thin film heater is used to joule heat a superconducting niobium line, then the switch can be operated, but the power consumption is high (about 50 μW)
Solution Approach 1:
The patent changes the material parameter of the superconducting switch from niobium (Tc = 9.2K) to titanium (Tc = 0.4K), which has a lower critical temperature. This parameter change allows the switch to be operated at lower temperatures, reducing the power required for heating and thereby resolving the contradiction between switch operability and power consumption.
Solution Approach 2:
The patent applies local quality by using different materials for different parts of the system: titanium for the switch element where low Tc is needed, and niobium for the heater and connections where high Tc is acceptable. This localized material selection optimizes the power consumption while maintaining the required functionality.
2Power
If a standard switch design with 100 μm × 100 μm overlap area is used, then the switch can be operated, but the inductance value is high
Solution Approach 1:
The patent transitions from a planar 2D overlap geometry to a folded 3D geometry for the superconducting switch. This dimensional change allows the current path to be folded back on itself, creating opposing magnetic fields that cancel each other, thereby reducing the overall inductance while maintaining the same footprint area.
Solution Approach 2:
The folded geometry introduces asymmetry in the current path configuration, where the current flows in opposite directions through different segments of the folded structure. This asymmetric arrangement creates opposing magnetic fluxes that cancel each other, reducing the net inductance of the switch.
3Ease of operation
If control signals are directly coupled to the quantum bit, then the control is simple, but the refrigerator is heated and noise is injected into the device
Solution Approach 1:
The patent introduces a superconducting persistent current switch as an intermediary between the control signal and the quantum bit. This intermediary allows the control signal to be transmitted without directly coupling to the qubit, thereby avoiding heating and noise injection while maintaining control functionality. The switch acts as a gate that can isolate or connect the control circuitry to the qubit as needed.
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 reduces power consumption by 80 times, minimizes inductance, and effectively attenuates noise currents, enabling precise control of magnetic flux bias points for quantum computation devices while maintaining low operating temperatures.
Implementation Method 1
a first current is applied to a heating element located proximate to a substantially titanium-formed switch element such that the switch element is warmed above a superconducting transition temperature
Implementation Method 2
the switch element is substantially formed from a material which exhibits a superconducting temperature value below a superconducting temperature value exhibited by a material used to provide a connection to the switch element
Data Source
AI summary
An improved persistent current switch design and method of operation are disclosed. By way of example, a persistent current switch circuit comprises a heating element and a switch element located proximate to the heating element, the switch element being substantially formed from a material (by way of example only, titanium) which exhibits a superconducting temperature value below a superconducting temperature value exhibited by a material (by way of example only, aluminum) used to provide a connection to the switch element. The switch element is responsive to the heating element such that the heating element is used to control whether or not the switch element is in a superconducting state. The switch element may also have a folded geometry. Such persistent current switches exhibit low power and low inductance.