Abstract
Building a large-scale quantum computer requires the co-optimization of both the quantum bits (qubits) and their control electronics. By operating the CMOS control circuits at cryogenic temperatures (cryo-CMOS), and hence in close proximity to the cryogenic solid-state qubits, a compact quantum-computing system can be achieved, thus promising scalability to the large number of qubits required in a practical application. This work presents a cryo-CMOS microwave signal generator for frequency-multiplexed control of 4 × 32 qubits (32 qubits per RF output). A digitally intensive architecture offering full programmability of phase, amplitude, and frequency of the output microwave pulses and a wideband RF front end operating from 2 to 20 GHz allow targeting both spin qubits and transmons. The controller comprises a qubit-phase-tracking direct digital synthesis (DDS) back end for coherent qubit control and a single-sideband (SSB) RF front end optimized for minimum leakage between the qubit channels. Fabricated in Intel 22-nm FinFET technology, it achieves a 48-dB SNR and 45-dB spurious-free dynamic range (SFDR) in a 1-GHz data bandwidth when operating at 3 K, thus enabling high-fidelity qubit control. By exploiting the on-chip 4096-instruction memory, the capability to translate quantum algorithms to microwave signals has been demonstrated by coherently controlling a spin qubit at both 14 and 18 GHz.
Highlights
Q UANTUM computers promise significant advantages over classical computers in solving several computing problems
A Monte Carlo simulation shows about a 3-dB loss in spurious-free dynamic range (SFDR) due to current source mismatch at 3 K, achieving ∼56-dB SFDR for a single tone
Due to the reduced bias current in the variable-gain amplifier (VGA), and the significantly large output transistor, achieving the required linearity over the full bandwidth is difficult, but it is ensured by adding a single-stage amplifier (PMOS differential pair with current-mirror load) that increases the loop gain and delivers the non-linear current required on the large mirror gate capacitance
Summary
Q UANTUM computers promise significant advantages over classical computers in solving several computing problems. As a stepping stone toward a scalable cryogenic electronic interface for a large-scale quantum processor, this works demonstrates a single-chip cryo-CMOS controller (operating at 3 K) optimized for controlling 128 qubits (operating at 20 mK) and requiring minimum interfacing to room-temperature equipment [18]. The focus is on the design of a controller operating at 3 K because of the higher available cooling power This does not restrict a future co-integration with qubits at the same temperature as the electronics since “hot” qubits operating at temperatures above 1 K have recently been demonstrated and are likely to evolve further in the few years [20], [21]. Compensate for the ac Stark shift in a frequency-multiplexing scheme [28]
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