NV centre & ODMR: diamond as a magnetometer (3D)
About this app
A nitrogen-vacancy centre in diamond: green laser, red fluorescence and a microwave scanning the spin resonance at 2.87 GHz. A magnetic field splits the resonance; in an ensemble four crystal axes show four projections from which the field vector follows.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
What it is about
The NV centre is a defect in the diamond lattice: a nitrogen atom sits next to a vacancy. In the negatively charged form NV⁻ two unpaired electrons form a spin S = 1. Without a magnetic field the states mₛ = ±1 lie D ≈ 2.87 GHz above mₛ = 0. A magnetic field shifts them by ±γ·B∥ with γ ≈ 28 GHz/T, and to first order only the component along the NV axis counts. Because this spin can be read out optically at room temperature, the NV centre is a quantum sensor for magnetic fields with resolution down to the nanometre range.
What the app shows
The app shows a section of the diamond lattice with nitrogen, vacancy and NV axis, a green 532 nm laser, the red glow and a microwave loop. The ODMR spectrum shows the fluorescence versus microwave frequency: where the frequency hits a spin transition, the NV gets darker. The app computes the transitions exactly from the spin Hamiltonian. A panel shows the spin levels and the optical cycle with the dark path via the singlet states.
What you can try
Sweep the frequency and watch the red glow fade at two points. Raise the field to 10 mT: the dips move apart, their spacing is 2·γ·B∥. Turn the field across the NV axis and the dips almost merge. An ensemble has four axis directions and up to eight dips; along a cube edge [100] there are only two, because all axes see the same magnitude of the projection.
Frequently asked questions
- What is an NV centre in diamond?
- An NV centre (nitrogen-vacancy centre) is a point defect in diamond: a nitrogen atom replaces a carbon atom and the neighbouring site is empty. In the NV⁻ charge state it has an electron spin S = 1 that can be polarised with green light and read out via its red fluorescence, even at room temperature.
- What does ODMR mean?
- ODMR stands for optically detected magnetic resonance. The NV centre is excited with a laser while a microwave frequency is swept. When it hits a transition from mₛ = 0 to mₛ = ±1, the fluorescence drops. The position of these dips reveals the magnetic field: f± = D ± γ·B∥ with D ≈ 2.87 GHz and γ ≈ 28 GHz/T.
- Does an NV centre measure the magnitude of the magnetic field?
- No, to first order it measures the component B∥ along its axis. A field across the axis shifts the lines only weakly. For the full field vector one uses ensembles with four ⟨111⟩ axis directions and reconstructs it from the four projections, with the signs fixed by a known bias field.
- What can I try in this app?
- You set magnitude and direction of the magnetic field, sweep the microwave frequency and read the dips in a table. You switch between a single NV and an ensemble, turn laser and microwave off and look at spin levels and the optical cycle. Explain mode walks you through the measuring principle step by step.
Subject: Quantum sensing
More from Quantum sensing
A VisuApp by heyprof: interactive, free in your browser, no sign-up. What is a VisuApp? · All apps