/Measurements beyond the standard quantum limit achieved at the center of a diamond’s nitrogen vacancy (via Qpute.com)
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Measurements beyond the standard quantum limit achieved at the center of a diamond’s nitrogen vacancy (via Qpute.com)

Figure 1 Dynamics and control of a single NV center. (A) Diagram of a single diamond-shaped NV center. It is driven by a variety of laser beams and coherently controlled by MW and RF pulses. Squared: Squared 532 nm green laser for reading NV electron spins and mixed charge states. Chopped: A chopped laser sequence for better polarization of electron spins without destroying the charge state. Powerful: Powerful (4 μW) 594 nm orange laser for reading charge states with real-time feedback. Weak: Weak (0.18 μW) orange laser for single-shot readout in a charged state. The NV electron spin (S = 1), the accompanying 14N nuclear spin (I = 1), and one of the randomly distributed 13C nuclear spins (I = 1/2) make up the interferometer. (B) Negative and neutral level diagrams of NV, indicated by NV- and NV0, and the corresponding dynamics driven by a 532 nm green laser and a 594 nm orange laser. (C) NV-Ground state spin level structure of triplets. MW and RF pulses are used to coherently manipulate NV electron spins and two nuclear spins (14N and 13C). (D) Projection measurement of 13C nuclear spin. The dashed line indicates the threshold for determining which state it stays in. Credit: DOI: 10.1126 / sciadv.abg9204

Many measurements are limited by standard quantum limits (SQL). SQL is defined as the measured noise level set by quantum mechanics. Quantum entanglement can be used to defeat SQL and approach the ultimate limit called the Heisenberg limit (HL). Sub-SQL measurements are implemented on many systems under extreme conditions, and the sensors in these systems are not suitable for realistic measurements under ambient conditions.

The nitrogen vacancy (NV) center of diamond can be used as a sensor for electron and nuclear magnetic resonance.They can work with Environmental condition To protect the solid crystal lattice. The entire sub-SQL measurement process based on a single NV center includes NV spin initialization and entanglement. Ambient conditions, Physical quantity detection, and reading of results. There was a problem with NV initialization and entanglement.

A research team led by Professor Du Jiangfeng of the University of Science and Technology of China (USTC) at the University of Science and Technology of China (USTC) uses the NV Center of Diamonds to achieve sub-SQL measurements under ambient conditions and uses intertwined sensors. It will defeat SQL and provide more accurate measurements.This study was published in Science Advances..

Researchers have applied real-time feedback technology to initialize spins to a high-purity state, faithfully achieving NV-charged states, electron spins, and joint initialization of two nuclear spins.

They replaced the squared pulsed laser with a chopped laser sequence for polarization of electron spins and improved the corresponding laser fidelity from 90% to 97.7%.

In addition, the researchers optimized the experimental setup to better control the experimental conditions. Sophisticated configuration for thermal separation and appropriate proportional integral differential (PID) parameters for feedback provide a very stable magnetic field with relatively low temperature fluctuations of 0.5 mK during the experiment and 1 ppm volatile. Realized.

This research opens new perspectives in the study of solid-state spin systems and lays the foundation for quantum sensing and computing.

The era of silicon carbide single spin color centers is approaching

For more information:
Tianyu Xie et al breaks standard quantum limits under ambient conditions with solid-state spins, Science Advances (2021). DOI: 10.1126 / sciadv.abg9204

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Measurements beyond the standard quantum limit achieved at the center of a diamond’s nitrogen vacancy

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