Frequency Multiplexing for Qubit Readout Lines
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Solution Overview
Problem
The existing technologies for reading out signals from a quantum processor with multiple qubits are limited by the number of lines required between the measurement and control unit and the qubits, which restricts the number of qubits that can be accommodated in a refrigerated environment due to the need for separate lines for each qubit, leading to challenges in scalability and fault tolerance.
Innovation Solution
The implementation of frequency multiplexing architecture that combines the output signals of multiple qubits into a single output, using a multiplexor (MUX) with 90-degree hybrid couplers and quantum-limited amplifiers, such as Josephson parametric converters (JPCs) and traveling wave parametric amplifiers (TWPAs), to reduce the number of lines needed, allowing for more qubits to be read out efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If frequency multiplexing is implemented to combine multiple qubit outputs into a single line, then the number of lines required is reduced, but the device complexity increases due to the need for multiplexors and hybrid couplers
Solution Approach 1:
Multiple qubit output lines are merged into a single line using frequency multiplexing. The patent combines outputs from multiple qubits (e.g., 8 qubits) onto one transmission line by assigning each qubit a unique frequency, thereby reducing the total number of lines required while maintaining individual signal integrity through frequency discrimination.
Solution Approach 2:
A single transmission line serves multiple functions by carrying signals from multiple qubits simultaneously. The multiplexor structure enables one line to handle multiple qubit readout channels, making the line multi-functional and reducing the overall connection count between the quantum processor and measurement equipment.
2Measurement precision
If quantum-limited amplifiers are used to enhance signal-to-noise ratio, then measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
Quantum-limited amplifiers act as intermediary components between the qubit output and the measurement equipment. These amplifiers (such as Josephson parametric converters or traveling wave parametric amplifiers) are positioned at the output of each qubit channel to amplify weak quantum signals before they encounter thermal noise, thereby improving measurement precision without requiring changes to the fundamental measurement architecture.
3Productivity
If more qubits are accommodated in the refrigerated environment, then computational power is increased, but the access limitations through the bulkhead opening become more severe
Solution Approach 1:
The patent transitions from a spatial dimension solution (adding more physical lines through the bulkhead) to a frequency dimension solution. By encoding multiple qubit signals at different frequencies on a single transmission line, the system accommodates more qubits without requiring additional physical access paths through the bulkhead opening, effectively using the frequency domain to overcome physical access limitations.
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 significantly reduces the number of lines required, enabling the accommodation of a larger number of qubits in a refrigerated environment, improving computational power and reliability by enhancing signal-to-noise ratio and fault tolerance through efficient signal processing and amplification.
Implementation Method 1
A quantum-limited amplifier is coupled to an output of the isolator and configured to provide an output of the qubit
Implementation Method 2
the quantum-limited amplifier is a Josephson parametric converter (JPC)
Implementation Method 3
the quantum-limited amplifier is a traveling wave parametric amplifier (TWPA)
Implementation Method 4
The MUX comprises one or more 90-degree hybrid couplers
Implementation Method 5
A circulator is coupled to an output of the filter and operative to receive a control signal
Implementation Method 6
the quantum processor, the MUX, and the filter, circulator and quantum-limited amplifier of each qubit, are configured in a dilution refrigerator
Data Source
AI summary
A system includes a quantum processor includes a plurality of qubits. For each qubit, there is a circulator operative to receive a control signal and an output signal from the qubit. An isolator is coupled to an output of the circulator. A quantum-limited amplifier is coupled to an output of the isolator and configured to provide an output of the qubit. A multiplexor (MUX) is configured to frequency multiplex the outputs of at least two of the plurality of qubits as a single output of the quantum processor.