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Nitrogen Vacancy center quantum sensors
Nitrogen Vacancy center quantum sensors
Quantum changes are difficult to measure without influencing the system, but trapping the quantum state in a diamond allows precise detection with minimal disturbance. This enables highly sensitive detection of small magnetic field changes with minimal interference
This technique works by knocking out two carbon atoms from a diamond, and then replacing one with a Nitrogen atom and leaving the other space vacant. This nitrogen and vacancy, create a strong localized magnetic field, which enables nanoscale detection of single molecules and cellular structures.
The goal of this technique would be to arrive to a precision that can determine the structure of transmembrane properties and diverse metabolic studies. Nano diamonds containing NV-centers can also locally probe temperature dependent biological processes in cells and small organisms such as cell development and endogenous heat generation, this because it can be done at room temperature.
Details of the diamond
Details of the diamond
A diamond is a carbon crystal with each carbon atom inside the lattice bond to four other carbon atoms. This rigid bond, gives the diamond it’s hard and compact structure. If there are distortions in the lattice, a carbon atom can be replaced by a Nitrogen, Silicon or Boron element. The lattice distortions give the diamonds their colors (ex. High concentrations of N give yellow diamonds).
If there is a diamond lattice defect, where an N atom is in the lattice bonded to three carbons and empty space (called vacancy), a nitrogen-vacancy center is created, of about 4-5nm. There are three different states created (positive, negative and neutral). The useful one for neuroimaging techniques is the NV negative center, which consist of 6 electrons inside its lattice.
Spin values of NV negative centers
Spin values of NV negative centers
Knowing that the spin of an atom:
Has an angular momentum, fundamental to the particle's nature
Is quantized (measured in discrete values without a unit)
Can be manipulated using microwaves and laser pulses
The phenomenon of a quantum system evolving in a predictable and reversible manner is called coherence. This coherence allows us to observe how the quantum system interacts with the external environment. However, the more one tries to measure a quantum system, the faster it loses coherence—a phenomenon known as decoherence.
In the case of the NV (nitrogen-vacancy) center in diamond, the surrounding diamond lattice isolates the trapped electron, preserving its spin coherence over time, even at room temperature. (Lowering the temperature may further enhance coherence, enabling even more precise measurements.)
When the NV center is hit with an energetic 532 nm green laser pulse, it excites the electron without altering its spin value. The excited electron eventually returns to its ground state, and the path it takes depends on the spin state. Simplified: if the spin is one value, the electron is more likely to emit a red photon; if the spin is another value, it emits a different photon.
By measuring the intensity of the emitted red light, the spin values of the NV center can be determined. Changes in light intensity directly correlate with changes in spin values. This process is called optically detected magnetic resonance (ODMR).
The image illustrates how NV centers emit different photons of varying wave lengths depending on their spin states. External magnetic fields influence the NV center’s spin and, thus, its light emission in a predictable way. Measuring these changes allows us to map out magnetic fields with high sensitivity.
For more information on research on quantum sensing with single spins in diamond, checkout the ETHZ spin diamond laboratory (spin physics department): https://spin.ethz.ch
referenceimage [1] https://www.quantumsensors.org/news/2020/12/07/new-spin-out-partnership-signals-quantum-leap-for-brain-imagingimage [2] https://www.sciencedirect.com/science/article/pii/S0079656522000322image [3] https://www.youtube.com/watch?v=CRfTe9gBOQA Quantum Sensing With a Special Synthetic Diamond
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