Electronic Noise Considerations for Designing Integrated Solid-State Quantum Memories

TL;DR

The work addresses the challenge of designing integrated control electronics for solid-state quantum memories by quantifying how local-oscillator noise couples to environmental dephasing in NV center qubits. It adopts a filter-transfer function framework to relate qubit coherence to noise spectra and dynamical decoupling filter functions, and validates the approach with NV experiments. Key contributions include experimentally confirmed predictions of coherence times from measured phase spectra and a practical method for deriving oscillator-noise targets and timing-jitter budgets for integrated control hardware, with clear guidance for other solid-state qubits and sensing platforms. The results enable hardware co-design that balances phase stability, bandwidth, and power consumption to support scalable quantum memories.

Abstract

As quantum networks expand and are deployed outside research laboratories, a need arises to design and integrate compact control electronics for each memory node. It is essential to understand the performance requirements for such systems, especially concerning tolerable levels of noise, since these specifications dramatically affect a system's design complexity and cost. Here, using an approach that can be easily generalized across quantum-hardware platforms, we present a case study based on nitrogen-vacancy (NV) centers in diamond. We model and experimentally verify the effects of phase noise and timing jitter in the control system in conjunction with the spin qubit's environmental noise. We further consider the impact of different phase noise characteristics on the fidelity of dynamical decoupling sequences. The results demonstrate a procedure to specify design requirements for integrated quantum control signal generators for solid-state spin qubits, depending on their coherence time, intrinsic noise spectrum, and required fidelity.

Figures (13)

• Figure 1: Effects of oscillator noise on a central spin.a, Schematic representation of effects of phase fluctuations on axes of rotation for a central spin, where phase fluctuations (faded curve) lead to fluctuations in the rotation axes (faded axes). b, System diagram of a quantum measurement setup incorporating an integrated signal general for an optically addressed spin qubit.
• Figure 2: Decoherence from environmental spin baths.a, Noise power spectral densities calculated for $^{13}$C nuclear spin bath (blue) and nitrogen electron spin bath (red). Dashed lines denote the respective correlation frequency for carbon nuclear spin bath and nitrogen electron spin bath. Dot-dashed line denotes the inhomogenously broadened decoherence rate measured for the studied sample. b-c, Decoherence envelopes calculated from $^{13}$C nuclear spin bath noise power spectral density in (a) for (b) free-induction decay and (c) spin-echo, with a predicted $T^\ast_2 = 1.95µs$ and $T_2 = 839µs$.
• Figure 3: Control sequences as filter-transfer functions.a, filter-transfer function of a spin-echo sequence with 100µs evolution time (maroon, right axis) plotted against the phase spectra of the $^{13}$C nuclear spin bath in conjunction with low-noise local oscillator (black, left axis) and noisy local oscillator (blue). b, CPMG-$N$ sequences represented as filter-transfer functions for a fixed total evolution time of 100µs, where $N$ signifies the number of $\pi$-pulses.
• Figure 4: Schematic diagram of rf control signal delivery setup.a, Experimental setup to deliver the rf control signal using a benchtop frequency synthesizer. b, Experimental setup to inject noise into the rf control signal, where the phase and frequency of an integrated voltage-controlled oscillator (VCO) is locked to an external frequency synthesizer through a phase-locked loop (PLL). The integrated VCO, off-chip PLL, and amplifier are interfaced through a custom printed circuit board (PCB).
• Figure 5: Effects of phase noise on measured coherence.a, Measured phase spectra of noise-injected local oscillator (solid traces) and reported phase spectrum of low-noise local oscillator (purple, dashed), combined with noise spectrum of $^{13}$C nuclear spin bath (shaded grey). b, Free-induction decay envelopes calculated from combined noise spectra for noisy local-oscillator in (a). Dot-dashed line denotes the dephasing threshold. c, Measured (errorbars) and calculated (orange solid line) $T^\ast_2$ times, with upper and lower bounds propagated from phase noise measurement uncertainty (shaded light orange). d, spin-echo decay envelopes calculated from combined noise spectra for noisy local-oscillator in (a). Dot-dashed line denotes the dephasing threshold. e, Measured (errorbars) and calculated (orange solid line) spin-echo $T_2$ times, with upper and lower bounds propagated from phase noise measurement uncertainty (shaded light orange).