A CMOS-Integrated Color Center Pulse-Sequence Control and Detection System

Abstract

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.