Figure 1

(a) Quantum memory circuit. The resonator, with frequency ${\omega }_c$ and damping rate $\kappa$ tunable at the nanosecond scale, is coupled to the spin ensemble (frequency ${\omega }_s$) with an ensemble coupling constant $g_{\mathrm{ens}}$. Drive pulses of amplitude $\beta (t)$ are applied to the spins via the resonator, which can be initialized in a well-defined quantum state $|\alpha ⟩$. (b) Amplitude of the microwave field generated by a coplanar resonator with quality factor $Q=100$ and driven by a pulse of $100\mu \mathrm{W}$ power. A static magnetic field ${\mathbf{B}}_{\mathrm{NV}}$ is applied parallel to the spins, which are distributed uniformly throughout the crystal. (c) Subensemble distribution $f(\Delta )$ of spin-resonance frequencies (circles) consisting of three hyperfine-split Lorentzian lines. The solid line shows the excitation probability for the chosen secant hyperbolic inversion pulses (see text). (d) The solid line shows calculated coupling-strength distribution function $\rho (g)g^2$. The histogram and circles show the subensemble distribution used in the calculation. The low- and high-frequency cutoffs in $\rho (g)$ originate from, respectively, high ($40\mu \mathrm{m}$) and low ($0.5\mu \mathrm{m}$) cutoffs in the distance from the resonator to NV centers.Reuse & Permissions

Figure 2

(a) Schematic timing of pulses and cavity parameters ${\Delta }_{cs}$ and $\kappa$. Periods of resonance (${\Delta }_{cs}=0$) are marked by gray areas. (b) Cavity-field mean values $X_c$ (black) and $P_c$ (gray) versus time. The inset replots the dashed-line region with $|⟨{\widehat{a}}_c⟩|$ on the logarithmic vertical scale. (c) The $g$-weighted transverse-spin-component mean value $S_{\perp }^{\mathrm{eff}}=\sqrt{S_x^{\mathrm{eff}2}+S_y^{\mathrm{eff}2}}$ (black) normalized to $N$, the excitation probability $p_{\mathrm{exc}}$ (gray, dashed curve), and the $g$-weighted excitation probability $p_{\mathrm{exc}}^{\mathrm{eff}}$ (gray, solid curve).Reuse & Permissions

Figure 3

(a) Summed variance of cavity-field quadratures. (b) The summed, $g$-weighted spin-component variance normalized to $2N$. (c) Various input states (black) and output states (gray, sign reversed) examined in the protocol. The centers of circles mark mean values whereas the radii mark the standard deviation $\sigma$ of the state. (d) Open symbols: the dependence of gain $\mathcal{G}$ (blue triangles), qubit fidelity $F_q$ (magenta circles), effective excitation probability $p_{\mathrm{exc}}^{\mathrm{eff}}$ (red squares), and summed variance $2{\sigma }^2$ (green diamonds) on the peak power $P_{\mathrm{peak}}$ of the external driving field during inversion pulses. Closed symbols: simulations with $P_{\mathrm{peak}}=100\mu \mathrm{W}$ and homogeneous coupling $g=2\pi \times 12.5\mathrm{Hz}$, leading to $\mathcal{G}=0.82$, $2{\sigma }^2=1.02$, and $F_q=87\%$.Reuse & Permissions

Figure 4

The cavity field $|a_c|$ versus time in a multimode storage example with four input fields $|a_c|=3$, 0, 1, 2) separated by $0.29\mu \mathrm{s}$, with memory time $12\mu \mathrm{s}$. The amplitude cross talk is below 3%.Reuse & Permissions