Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Digital Predistortion of Power Amplifiers for Quantum Computing

Marvin Jaeger, Bartosz Tegowski, Georg Frederik Riemschneider, Alexander Koelpin

TL;DR

The paper addresses PA-induced nonlinearity and memory effects as a key source of quantum-gate errors in microwave-controlled quantum computers. It proposes integrating digital predistortion (DPD) with a feedback loop into the quantum-control signal generator to linearize the RF chain without excessive input back-off. Using a memory-polynomial DPD with coefficients estimated from a PA feedback path, the authors demonstrate through numerical qubit simulations that predistorted control signals yield higher qubit fidelity (e.g., from $F=99.4\%$ to $F=99.81\%$ for an exemplary sequence) and reduced infidelity across output powers. This approach suggests a path to faster, more power-efficient quantum computation by compensating RF-path nonlinearities in real-world control hardware.

Abstract

Power amplifiers (PA) are essential for microwavecontrolled trapped-ion and semiconductor spin based quantum computers (QC). They adjust the power level of the control signal and therefore the processing time of the QC. Their nonlinearities and memory effects degrade the signal quality and, thus, the fidelity of qubit gate operations. Driving the PA with a significant input power back-off reduces nonlinear effects but is neither power-efficient nor cost-effective. To overcome this limitation, this letter augments the conventional signal generation system applied in QCs by digital predistortion (DPD) to linearize the radio frequency (RF) channel. Numerical analysis of the qubit behavior based on measured representative control signals indicates that DPD improves its fidelity.

Digital Predistortion of Power Amplifiers for Quantum Computing

TL;DR

The paper addresses PA-induced nonlinearity and memory effects as a key source of quantum-gate errors in microwave-controlled quantum computers. It proposes integrating digital predistortion (DPD) with a feedback loop into the quantum-control signal generator to linearize the RF chain without excessive input back-off. Using a memory-polynomial DPD with coefficients estimated from a PA feedback path, the authors demonstrate through numerical qubit simulations that predistorted control signals yield higher qubit fidelity (e.g., from to for an exemplary sequence) and reduced infidelity across output powers. This approach suggests a path to faster, more power-efficient quantum computation by compensating RF-path nonlinearities in real-world control hardware.

Abstract

Power amplifiers (PA) are essential for microwavecontrolled trapped-ion and semiconductor spin based quantum computers (QC). They adjust the power level of the control signal and therefore the processing time of the QC. Their nonlinearities and memory effects degrade the signal quality and, thus, the fidelity of qubit gate operations. Driving the PA with a significant input power back-off reduces nonlinear effects but is neither power-efficient nor cost-effective. To overcome this limitation, this letter augments the conventional signal generation system applied in QCs by digital predistortion (DPD) to linearize the radio frequency (RF) channel. Numerical analysis of the qubit behavior based on measured representative control signals indicates that DPD improves its fidelity.
Paper Structure (8 sections, 10 equations, 4 figures)

This paper contains 8 sections, 10 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Qubit Gate Operation
  3. Quantum Control Signal Generation
  4. Experimental Results
  5. Experimental Setup
  6. State-Fidelity Analysis of an Exemplary Sequence
  7. Analysis Over Output Power
  8. Conclusion

Figures (4)

  • Figure 1: Conceptual transmitter architecture of (a) a classical quantum control system and (b) a quantum control system extended by DPD and a feedback loop for PA characterization. The Bloch sphere visualizes the qubit state $\lvert \psi \rangle$.
  • Figure 2: (a) Ideal (blue) and distorted (red) magnitude of the equivalent baseband output signal. (b) Spectrum illustrating desired qubit excitations (yellow) and idle qubits (green).
  • Figure 3: Calculated trajectory of an exemplary sequence (idle, $Y_\pi$, $-X_\pi$, idle) within the Bloch sphere, calculated for qubit 1 based on measured control signals.
  • Figure 4: Mean infidelity versus normalized average output power of the different qubits, swept over a set of output powers.