Researchers at HZB have created an innovative method to detect quantum spin states in diamonds by using electrical signals rather than light, potentially simplifying quantum sensors and computing devices.

Diamonds with special optically active defects called color centers can function as sensitive sensors or quantum bits by storing information in their electron spins. Traditionally, detecting these spin states relies on complex optical techniques. Researchers at HZB have now introduced a simpler method that uses photovoltage to read the spin states of individual defects, potentially enabling much smaller and more compact quantum sensors.

Figure 1. Green Laser Excites NV Centers; Scanning Tip Measures Spin-Dependent Potential

Utilizing Defects to Detect Spin States

Defects in solids are usually considered flaws, but in diamonds, they provide unique benefits. By adding nitrogen vacancy (NV) centers to the crystal, researchers create defects with electron spin states that can be manipulated via microwaves. These spin states can store information, making NV-doped diamonds valuable both as highly sensitive sensors and as qubits for quantum computing. Figure 1 shows Green Laser Excites NV Centers; Scanning Tip Measures Spin-Dependent Potential.

Limitations of Optical Spin Detection

Previously, detecting the spin state of an NV center relied on capturing photons emitted by the defect. Because a spin flip usually produces only a single photon, the resulting signal is very weak, making the detection setup technically difficult and complex.

Voltage-Driven Breakthrough

A team at HZB tackled this challenge by leveraging the electrical charge of defect centers alongside their spin states, explains Dr. Boris Naydenov. They adapted Kelvin probe force microscopy (KPFM), a form of atomic force microscopy, to measure these charges. By using a laser to excite the NV centers, free charge carriers are generated, which interact with surface states and produce a detectable voltage around the NV center—enabling electrical detection of the spin state.

Detecting Spins via Electrical Charge

“The photovoltage varies with the electron spin state of the NV center, enabling the detection of individual spins,” explains Sergei Trofimov, who conducted the measurements during his PhD. Additionally, this new technique allows capturing spin dynamics by coherently controlling the spin states with microwave excitation.

Detecting Spins via Electrical Charge

“The photovoltage varies with the electron spin state of the NV center, enabling the detection of individual spins,” explains Sergei Trofimov, who conducted the measurements during his PhD. Additionally, this new technique allows capturing spin dynamics by coherently controlling the spin states with microwave excitation.

“This breakthrough paves the way for creating ultra-small, compact diamond-based devices that require only appropriate electrical contacts instead of complicated microscopic optics and single-photon detectors,” says Prof. Klaus Lips, head of the Spins in Energy Conversion and Quantum Information Science department [2]. He adds that the new readout technique could also be applied to other solid-state systems where electron spin resonance of defects is observed.

References:

1. https://scitechdaily.com/tiny-diamonds-big-spark-a-laser-free-leap-in-quantum-spin-detection/
2. https://lifeboat.com/blog/2025/04/tiny-diamonds-big-spark-a-laser-free-leap-in-quantum-spin-detection

Cite this article:

Janani R (2025), Tiny Diamonds, Major Breakthrough: Laser-Free Quantum Spin Detection, AnaTechMaz, pp.254