Sensing of Arbitrary-Frequency Fields Using a Quantum Mixer

Abstract

Quantum sensors such as spin defects in diamond have achieved excellent performance by combining high sensitivity with spatial resolution. Unfortunately, these sensors can only detect signal fields with frequency in a few accessible ranges, typically low frequencies up to the experimentally achievable control field amplitudes and a narrow window around the sensors’ resonance frequency. Here, we develop and demonstrate a technique for sensing arbitrary-frequency signals by using the sensor qubit as a quantum frequency mixer, enabling a variety of sensing applications. The technique leverages nonlinear effects in periodically driven (Floquet) quantum systems to achieve quantum frequency mixing of the signal and an applied bias ac field. The frequency-mixed field can be detected using well-developed sensing techniques such as Rabi and CPMG with the only additional requirement of the bias field. We further show that the frequency mixing can distinguish vectorial components of an oscillating signal field, thus enabling arbitrary-frequency vector magnetometry. We experimentally demonstrate this protocol with nitrogen-vacancy centers in diamond to sense a 150-MHz signal field, proving the versatility of the quantum mixer sensing technique.

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Plain Language Summary

Harnessing the power of quantum coherence and entanglement, quantum sensors have achieved the most sensitive measurement of various signal fields, often with atomic-scale spatial resolution. However, the accessible frequency range of these signals is still limited by the sensors’ resonance frequency or achievable control field amplitudes—a remaining obstacle to their broad applications. To overcome this limitation, we develop a technique to sense arbitrary frequency signal fields using an integrated sensor and mixer, both based on the same quantum device.

By exploiting virtual transitions in the Fourier frequency space of periodically driven quantum systems, we create the quantum analog of a frequency mixer. By applying a bias ac field, the signal frequency is converted to the accessible frequency range for the quantum sensor, allowing it to be probed with well-developed sensing protocols. Furthermore, our technique can distinguish vectorial components of an oscillating signal field, thus enabling vector magnetometry at arbitrary frequencies. Experimentally, we use solid-state spin defects in diamond to demonstrate our technique by sensing a 150-MHz vector magnetic signal, which is outside the range usually accessible by such a sensor.

Because our technique integrates the quantum mixing function within existing quantum sensors, it can be broadly applied in many physical platforms, extending their frequency range while retaining all their exquisite properties. In addition, frequency mixing could be used in other contexts—from quantum simulation to quantum control—taking advantage of our robust theoretical framework. We envision that protocols based on quantum frequency mixing will be important tools in many quantum fields and devices.