Persistent Current Flux Bias Loops for Low-Heat Tunable Transmons
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Solution Overview
Problem
In superconducting quantum computing, flux tunable qubits face issues with unwanted heating and cross-talk due to DC currents used to generate magnetic flux, leading to inefficiencies and operational challenges in cryostats.
Innovation Solution
A quantum circuit device with a qubit chip featuring a lattice structure of fixed frequency transmon qubits coupled to flux tunable transmon couplers, utilizing a superconducting wiring layer with inductively coupled loops and bias lines made of different materials to reduce current flow into the cryostat, generate persistent currents, and minimize entanglement between qubits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DC current is applied to flux tunable transmon to adjust frequency, then magnetic flux control is achieved, but unwanted heating and ground loops are generated
Solution Approach 1:
The flux bias system is segmented into multiple independent flux bias lines, each controlling specific flux tunable elements. This allows selective application of DC current only where needed for frequency tuning, rather than applying current globally through a single bias line, thereby reducing unwanted heating and ground loops in other parts of the circuit.
Solution Approach 2:
A persistent current loop is introduced as an intermediary element between the flux bias line and the flux tunable transmon. The persistent current loop converts the applied DC current into a stable magnetic flux offset without requiring continuous DC current flow through the cryostat, thereby eliminating steady-state heating while maintaining frequency tuning capability.
2Reliability
If DC current is increased to achieve minimum ZZ exchange between qubits, then entanglement control is improved, but heat generation in cryostat increases
Solution Approach 1:
A persistent current is established in advance in the loop before qubit operations begin. This preliminary action creates a stable magnetic flux offset that enables proper ZZ exchange control between qubits without requiring continuous high DC current during operation, thereby reducing heat generation while maintaining entanglement control.
Solution Approach 2:
The system changes the operational parameter from continuous DC current flow to persistent current in a superconducting loop. By exploiting the zero-resistance property of superconductors, the flux bias is maintained without continuous energy input, reducing heat generation while preserving the ability to control ZZ exchange between qubits.
3Ease of manufacture
If flux bias line uses same superconducting material as loop, then manufacturing is simplified, but cross-talk between components increases
Solution Approach 1:
Different superconducting materials with different critical temperatures are used for the flux bias line and the persistent current loop. This local differentiation in material properties allows optimization of each component's performance: the flux bias line material is selected for low loss and stability, while the loop material is selected for its persistent current characteristics, thereby reducing cross-talk between components.
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 heat generation and cross-talk, maintaining the superconducting components within an operable temperature range while minimizing entanglement between qubits, resulting in a more efficient and less complicated quantum circuit operation.
Implementation Method 1
A flux bias line constructed of a superconducting material that is different than the superconducting material of the loop, wherein the flux bias line is inductively coupled to both the loop and the flux tunable transmon
Implementation Method 2
A DC current flows through a superconducting wire that is adjacent to the flux tunable transmon to generate an evanescent magnetic field that produces the flux
Implementation Method 3
A wiring layer is coupled to the qubit chip, wherein the wiring layer includes a loop constructed of a superconducting material
Data Source
AI summary
A quantum circuit device includes a qubit chip including a plurality of qubits and a plurality of flux tunable couplers. A plurality of fixed frequency qubits are arranged in in a lattice structure, wherein each pair of the plurality of fixed frequency qubits is coupled to one flux tunable coupler. A wiring layer is coupled to the qubit chip, and the wiring layer includes a loop constructed of a superconducting material that is inductively coupled to the flux tunable couplers. A flux bias line is constructed of a superconducting material that is different than the superconducting material of the loop, wherein the flux bias line is inductively coupled to both the loop and the flux tunable couplers.