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Digital predistortion of power amplifiers for quantum computing

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

Published Sep 1, 2026• 0 citations
Publisher

Abstract

Power amplifiers (PA) are essential for microwave-controlled 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.

DOI
10.15480/882.18416

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Power amplifiers (PA) are essential for microwave-controlled 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.
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.
Flux-tunable superconducting qubits rely on fast flux control pulses to implement two-qubit entangling quantum gates, a key building block for quantum algorithms. However, distortion effects introduced by non-ideal control electronics, parasitic components, and the cryogenic quantum chip response can all degrade the gate fidelity. We present a digital predistortion (DPD) framework for characterizing and then compensating for these distortions using a combination of infinite impulse response (IIR) and finite impulse response (FIR) filters. Experiments on a flux-tunable quantum processing unit (QPU) demonstrate a successful correction of step-response distortions on the flux-control line, with a compensated control signal showing only sub-percent deviations from the ideal target linear behavior. The demonstrated method enables automated rapid calibration of flux control channels for superconducting QPUs.
This work presents a power amplifier (PA) for microwave-driven entanglement operation in ion-trap-based Ytterbium qubit gates. The design is optimized for a center frequency of 13 GHz with a 3 dB bandwidth of 6 GHz thereby fulfilling the requirements to drive the 12.6 GHz hyperfine transisiton in the electronic ground state of a171Yb+ion. The PA achieves a saturated output power of 14 dBm and a gain of 20 dB at the center frequency. Due to a tunable operating point it is possible to realize a power-efficient amplitude modulation allowing for a qubit-gate fidelity improvement. The presented circuit achieves a measured power-added-efficiency (PAE) of 28 %. Due to maintaining an electrically stable operation during operation-point changes, this circuit is highly suitable for analyzing the effect of various pulse envelopes on the gate fidelity. The proposed circuit is silicon-proven and fabricated in a 0.13 µm SiGe BiCMOS process covering a core area of only 0.14 mm2.
High-fidelity quantum gates require precise classical control signals, yet the analog hardware delivering these signals introduces nonlinear distortions that degrade gate performance. We demonstrate digital predistortion of an acousto-optic modulator used to generate multi-tone entangling-gate waveforms in a trapped-ion processor based on 88^{88}88Sr+^++. By measuring and inverting the static nonlinear amplitude response of the modulator, we apply a feed-forward correction that extends its linear operating range and suppresses spurious intermodulation products. Spectral analysis of the gate beam shows 3--5 dB suppression of the dominant intermodulation tones, approximately doubling the usable diffraction efficiency at a 10−310^{-3}10−3 estimated gate-error threshold. Direct two-qubit Bell-state fidelity measurements confirm that predistortion consistently improves entangling-gate performance. The calibrate-and-invert methodology is device and platform agnostic, applicable to any nonlinear element in the classical control chain of a quantum processor.
In quantum computing, control signals are susceptible to distortion during transmission. Transmission distortion introduces residual voltages that degrade fidelity of quantum operations. Conventional pre-storage calibration need prohibitive memory and latency costs. We present a real-time predistortion circuit based on Infinite Impulse Response(IIR) Filter in 28 nm CMOS that synthesizes the corrected waveforms directly on chip, eliminating offline computation. And this architecture downloads input envelopes only instead of complete waveforms. The architecture supports arbitrary durations for specific pulse types such as rectangular pulses at 3 GSa/s wthin acceptable precision, which establishes the foundation for memory-efficient control in quantum computing.
Precise manipulation of a quantum bit (qubit) magnetic dipole moment requires exact control over the radiofrequency (RF) excitation field amplitude, pulse envelope, and duration. This paper presents a complete analytical derivation linking target quantum logic gate flip angles (α = π/2, π) to the necessary physical RF power amplifier (PA) parameters—specifically voltage gain (G) and peak output power (P ). Starting from a digital direct synthesis (DDS) driving model, we map unitless digital baseband signals through a digital-to-analog converter (DAC) and an impedance-matched resonant LC tank into the physical transverse magnetic field (B1). Applying a coordinate transformation to the rotating frame under the Rotating Wave Approximation (RWA) and modeling Gaussian pulse truncation (τ = nσ), closed-form expressions are derivedfor G and P . This analytical framework provides a direct link between physical hardware specifications and target quantum state rotations.