Low-Loss Broadband Antenna for Efficient Photon Collection from a Coherent Spin in Diamond

We report the creation of a low-loss broadband optical antenna giving highly directed output from a coherent single spin in the solid state. The device, a crystalline solid-state realization of a dielectric antenna, is engineered for individual nitrogen-vacancy electronic spins in diamond. We demonstrate a directionality close to 10. The photonic structure preserves the high spin coherence of single-crystal diamond ($T_2\gtrsim 100\mu \mathrm{s}$). The single-photon count rate approaches a megahertz facilitating efficient spin readout. We thus demonstrate a key enabling technology for quantum applications such as high-sensitivity magnetometry and long-distance spin entanglement.

Figure 1

(a) Schematic of the high-index dielectric antenna structure: a thin-diamond membrane containing NV centers is bonded to a gallium phosphide (GaP) SIL. The majority of the NV PL is emitted within the critical angle $\theta \sim 47°$ of the GaP-diamond interface [corresponding to emission within a numerical aperture (NA) of approximately 0.73]. (b) Positioning of the transferred diamond membranes onto the GaP SIL using a micromanipulator. (c) Room-temperature PL spectrum of a single-NV center collected through the dielectric antenna. PL studied in this work passes through a $(675\pm 50)\text{−}\mathrm{nm}$ bandpass filter to improve the signal-to-background ratio.

Figure 2

Angular radiation patterns of NV ensembles in the dielectric antenna obtained by back focal plane (BFP) imaging for (a) $d=815\mathrm{nm}$ and (c) $d=560\mathrm{nm}$. (b),(d) Average of the measured BFP images over azimuthal angle $\varphi$ and calculated emission patterns. (e) Broadband emission pattern of a single-NV center. (f) Calculated BFP image for a NV center in a diamond membrane with $d=155\mathrm{nm}$ and $h=140\mathrm{nm}$. The color bar applies to all images in the figure. (a)–(d) use a $(680\pm 5)\text{−}\mathrm{nm}$ bandpass filter; (e) a $(675\pm 50)\text{−}\mathrm{nm}$ bandpass filter.

Figure 3

(a) PL images of individual NV centers recorded through the SIL and through the backside of the antenna. (b) Photon autocorrelation measurement $g^{(2)}(t)$ of NV center no. 1 using pulsed excitation. The data show $g^{(2)}(0)\lesssim 0.1$ and an exponential PL decay with a lifetime $\tau =(15.4\pm 0.2)\mathrm{ns}$. (c) Comparison of PL saturation of a single NV in the dielectric antenna when detecting through the GaP SIL and through the backside of the antenna. NV PL is detected using a $(675\pm 50)\text{−}\mathrm{nm}$ bandpass filter.

Figure 4

(a) Optically detected magnetic resonance (ODMR) of the NVs highlighted in Fig. 3 ($|\overrightarrow{B}|\sim 4\mathrm{mT}$), each exhibiting a different orientation within the diamond lattice. The low ODMR contrast results from the low microwave power at the NV location. (b) ODMR amplitude of NV no. 1 imaged in the back focal plane. (c) Hahn spin-echo measurement on NV no. 4 yielding $T_2=(114\pm 9)\mu \mathrm{s}$ ($|\overrightarrow{B}|\sim 11.5\mathrm{mT}$).