Qubit Gate Capacitor Array Switching to Reduce Memory Effects
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Solution Overview
Problem
In quantum computing, transmitting and receiving a large number of signals to and from qubits is challenging due to the complexity of connections required, which can be mitigated by multiplexing signals onto fewer cables, but existing methods face issues with parasitic capacitance and memory effects in capacitor arrays.
Innovation Solution
A companion die with a capacitor array is used, where capacitors are charged by a digital-to-analog converter and switched to qubit gates one at a time, with control circuitry managing the switching to minimize parasitic capacitance effects and achieve desired voltage levels, using a multiplexer and decoder to efficiently connect capacitors to qubits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If signals are multiplexed onto fewer cables to reduce connections, then the number of connections to the quantum processor is reduced, but parasitic capacitance effects and memory errors increase
Solution Approach 1:
The patent divides the capacitor array into multiple individually controllable capacitors (C0, C1, C2, etc.), each capable of being switched independently to the qubit gate. This segmentation allows precise control over which capacitors are activated, enabling the system to manage parasitic capacitance effects by selectively engaging only the necessary capacitors rather than having all capacitors continuously connected.
Solution Approach 2:
The patent implements dynamic switching of capacitors to the qubit gate based on real-time signal requirements. The switch controller dynamically determines which capacitors to connect and for how long, adjusting the configuration adaptively to minimize parasitic capacitance effects while maintaining signal integrity. This dynamic approach contrasts with static connections that would always exhibit full parasitic capacitance.
2Reliability
If capacitors are switched one at a time to qubit gates, then parasitic capacitance effects are minimized, but the switching complexity and control requirements increase
Solution Approach 1:
The patent employs a single switch controller that performs multiple functions: it controls the timing of capacitor switching, selects which capacitors to connect, manages the charging/discharging sequences, and coordinates with the DAC. This multi-functional controller reduces the need for separate control circuits for each capacitor, thereby managing complexity while maintaining precise voltage control.
Solution Approach 2:
The capacitor array system uses its own internal structure to manage switching operations. The switch controller leverages the inherent properties of the capacitors and their connections to the qubit gate to automatically manage voltage distribution and minimize parasitic effects, reducing the need for external intervention or complex external control circuitry.
3Measurement precision
If multiple capacitors are connected to charge the parasitic capacitor, then desired voltage levels are achieved, but memory effects from previous voltages persist
Solution Approach 1:
The patent implements preliminary charging of capacitors through the DAC before they are switched to the qubit gate. By pre-charging capacitors to the desired voltage levels and then switching them simultaneously or in controlled sequences, the system ensures that each capacitor contributes the correct voltage amount, overcoming the influence of previous voltage states on the parasitic capacitor.
Solution Approach 2:
The patent employs periodic resetting and recharging of the capacitor array between different qubit operations. This periodic action clears any memory effects from previous operations by returning the capacitors to a known initial state, ensuring that each new operation starts with clean voltage conditions regardless of prior states.
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 the number of connections needed while minimizing errors due to parasitic capacitance, allowing for efficient signal transmission and reception with exponentially decreasing errors as more capacitors are switched, effectively reducing the complexity of quantum processor connections.
Implementation Method 1
a capacitor array comprising a plurality of capacitors; an output; a series capacitor between the capacitor array and the output
Implementation Method 2
capacitors in the capacitor array are charged to an output voltage of a digital-to-analog converter (DAC)
Implementation Method 3
switches couple the capacitors in the array to a gate of a qubit one at a time
Data Source
AI summary
Technologies for the reduction of memory effects in a capacitor are disclosed. In the illustrative embodiment, a companion chip is connected to a quantum processor. The companion chip provides voltages to gates of qubits on the quantum processor. The companion chip includes an array of capacitors that can be charged to a voltage based on a voltage to be applied to a gate of the quantum processor. The capacitors in the array of capacitors are connected to the gate one at a time, charging up a parasitic capacitance. As more capacitors are switched, the voltage on the gate approaches a target voltage with an exponentially-decreasing voltage error.