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.
T2∗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.
Color-center quantum bits (qubits), such as the Nitrogen-Vacancy center (NV) in diamond, have demonstrated entanglement between remote (>1.3km) qubits and excellent coherence times [1], all while operating at a few Kelvins. Compared to other qubit technologies typically operating at mK temperatures, the higher operating temperature of NVs enables scalable 3D integration with cryo-CMOS control electronics [2], provides significantly more cooling power, and removes the interconnect bottleneck between the qubits and the electronics in prior art [3–5]. Yet, no cryo-CMOS controller for NV-based quantum computers (QC) has been demonstrated.