Chip-Scale quantum magnetometry via CMOS integration with diamond color centers

I. Varveris

Jinchen Wang, Yuyang Han, Isaac Harris +5 more

We present a scalable cryo-CMOS controller for color-center-based quantum processors. A diamond waveguide micro-chiplet with NVs is pick-and-placed on CMOS with a 3D-printed prism for scalable photonic readout. A serial qubit driver array using grid inductors and pulse-width modulators generates a programmable 2.87GHz magnetic field for each qubit with low power and strong confinement. Up to 144 qubits can be operated on a single chip, with$204\mu\mathrm{W}$power consumption per qubit under active control.

Naufer Nusran, M. Ummal Momeen, M. V. Gurudev Dutt

Jinchen Wang, Isaac Harris, Xibi Chen +2 more

Color centers are defects within crystals that trap charge carriers in optically accessible levels. In diamonds, these color centers hold great potential for use in quantum sensing and quantum information. The utilization of the nitrogen vacancy (NV) center situated within diamond has allowed demonstrations of magnetic field, electric field, strain, and temperature sensors [1]. In more recent times, the investigation of color centers employing group-IV elements, such as SiV, GeV, and SnV, has gained interests [2]. This interest is attributed to their zero electric dipole moment and diminished optical transition fluctuations, as shown in Fig. 1. However, the manipulation and detection of color centers requires unwieldy and discrete commercial apparatus, leading to a large overall footprint and imposing constraints upon its practical utility. To address this issue, a CMOS-integrated quantum sensor based on loop inductors [3], and a quantum magnetometer using scalable inductor array and photonic filter [4] have been proposed for NV operating at room temperature (RT). In [3], the on-chip photonic filter attenuates the influence of the green laser excitation at a ratio of 10dB, concurrently with the on-chip photodiode (PD) detection of the red fluorescence stemming from the NV center excitation. [4] subsequently enhances this suppression to 25dB for green light. Nevertheless, both [3] and [4] suffer from the red fluorescence emitted by the top passivation on the CMOS chip, which is also excited by the laser (Fig. 2). The photonic filter cannot eliminate this undesired passivation layer's fluorescence because it shares the same frequency as the color center fluorescence. Thus, the top passivation layer must be etched before taking measurements. However, etching the passivation can introduce more defects in the underlying layers, leading to increased randomness and making it more challenging to control the fluorescence. Besides, the scope of effectiveness attributed to on-chip photonic filters encounters constraints in the context of other variants of color centers. The NV can be excited using an off-resonant 532 nm laser, and the intensity of the broad emission from 637 to 780nm is spin state dependent, allowing the scattered excitation light to be spectrally filtered during spin readout. The group IV emitters do not allow off-resonant readout of the spin state, so resonant excitation that matches the frequency of must be used, making spectral filtering more challenging, as shown in Fig. 1. This paper introduces a CMOS-integrated control and detection system capable of functioning at both room and cryogenic temperatures.

Niels Fakkel, Luc Enthoven, Jiwon Yun +9 more

Striving toward a scalable quantum processor, this article presents the first cryo-CMOS quantum bit (qubit) controller targeting color centers in diamond. Color-center qubits enable a modular architecture that allows for the 3-D integration of photonics, cryo-CMOS control electronics, and qubits in the same package. However, performing quantum operations in a scalable manner requires large currents in the driving coils due to low coil-to-qubit coupling. Moreover, active calibration of the qubit Larmor frequency is required to compensate inhomogeneities of the bias magnetic field. To overcome these challenges, this work proposes both a cryo-CMOS alternating current (AC) controller consisting of a class-DE series-resonant driver and a DC current regulator (DC CR) that uses a triode-biased H-bridge for scalable low-power qubit operations. By experimentally validating the cryo-CMOS performance with a nitrogen-vacancy (NV) color-center qubit, the AC controller can drive a Rabi oscillation up to 2.5 MHz with a supply draw of 6.5 mA, and the DC CR can tune the Larmor frequency by ±9 MHz while driving up to ±20 mA in the bias coil.$T_{2}^{*}$coherence times up to$5.3~\mu $s and single-qubit gate fidelities above 98% are demonstrated with the cryo-CMOS control using Ramsey experiments and gate set tomography (GST), respectively. The results demonstrate the efficacy of the proposed cryo-CMOS chips and enable the development of a modular quantum processor based on color centers.

H. Kurokawa, K. Sato, M. Kamata +16 more

Chip integration of quantum emitters is a crucial milestone for scalable quantum photonic information processing. Among optically active defect centers for quantum photonics, diamond color centers are promising because of their long spin coherence times and high photon emission rates. However, for a coherent-photon emission, they typically require a cryogenic environment to protect optical coherence from thermal phonons, which makes chip integration challenging. In this paper, we develop a chip-integrated diamond photonic crystal cavity embedding an ensemble of nitrogen-vacancy (NV) centers. We confirm cryogenic operation by observing Purcell enhancement of NV-center emission via an edge-coupled optical fiber. This result demonstrates successful integration of diamond color centers, a photonic crystal cavity, and an optical waveguide-fiber package, representing a key step toward scalable diamond-based quantum communication platforms.