NV-Center Diamond Magnetometer

Sensor Controls

External field B 0.0 mT

Microwave frequency 2870.0 MHz

Lattice temperature 300 K

Readout

Fluorescence

100%

Photon rate

high

Resonance f−

2870.0

Resonance f+

2870.0

Inferred field from splitting Δf = f+ − f− = 2γB

B_meas ≈ 0.00 mT

How it works

A nitrogen-vacancy (NV) centre is a point defect in diamond: a nitrogen atom next to a missing carbon atom. Its ground state is an electron spin triplet (S = 1) with sublevels m_s = 0, ±1. Spin–orbit coupling to the lattice produces a zero-field splitting even with no magnetic field:

D(T) ≈ D₀ + (dD/dT)(T − 300 K)
D₀ = 2870 MHz,  dD/dT ≈ −74 kHz/K

A green laser (532 nm) optically pumps the NV into m_s=0 and makes it fluoresce red. The m_s=0 state fluoresces brighter than m_s=±1, because m_s=±1 can decay through a dark, non-radiative shelving state. A microwave field resonant with the 0→±1 transition pumps population out of the bright state, so fluorescence dips exactly at resonance — this is optically detected magnetic resonance (ODMR).

An external field B along the NV axis Zeeman-splits the ±1 sublevels by ±γB (γ ≈ 28 MHz/mT for an electron spin), giving two dips instead of one:

f− = D(T) − γB
f+ = D(T) + γB
Δf = f+ − f− = 2γB  →  B = Δf / (2γ)

Measuring the dip splitting is a direct, calibration-free readout of B — this is the operating principle behind real NV-diamond magnetometers, which reach nanotesla to picotesla sensitivity in the lab (this demo uses millitesla-scale fields so the splitting stays visible on the slider). Turning the laser off removes the fluorescence signal entirely, since ODMR is an optical readout of a microwave transition.

Nitrogen Carbon lattice Vacancy Emitted photon

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