⚛️ quantum physics

A portable LED-based diamond magnetometer for outreach and teaching labs

This paper presents a compact, low-cost, and safe portable diamond magnetometer that utilizes a high-power LED instead of a laser, making it an ideal tool for educational outreach and undergraduate laboratories while maintaining the ability to generate ODMR spectra with a sensitivity of approximately 1 $\mu$ T/ $\sqrt{\text{Hz}}$ .

Original authors: Hollis Williams, Alex Newman, Stuart Graham, Colin Stephen, Gavin Morley

Published 2026-02-09

📖 4 min read🧠 Deep dive

CC BY 4.0

Original authors: Hollis Williams, Alex Newman, Stuart Graham, Colin Stephen, Gavin Morley

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you have a tiny, magical diamond that acts like a super-sensitive compass. Inside this diamond are special "defects" (missing atoms) that behave like tiny spinning tops. When you shine a green light on them, they glow red. But here's the trick: if you also blast them with invisible radio waves (microwaves) at just the right frequency, their red glow dims slightly. This dimming tells you exactly how strong the magnetic field around them is.

This is the core idea behind a Diamond Magnetometer. Usually, building one requires expensive, dangerous lasers and complex alignment, making it a "grown-up" tool for high-tech labs.

The Paper's Big Idea: The "Flashlight" Upgrade
The researchers from the University of Warwick decided to swap the scary, expensive laser for something much simpler: a super-bright green LED (like the kind in a high-powered flashlight or stage light).

Think of it like this:

The Old Way: Using a laser is like trying to thread a needle with a high-powered spotlight. It's precise, but if you sneeze, the whole thing breaks, and you need safety goggles and a locked room.
The New Way: Using the LED is like using a bright, steady desk lamp. It's safe, cheap, and you can look right at it without fear.

How It Works (The "Kitchen Sink" Setup)
The device is built to be portable and easy to assemble, almost like a science kit for university students or public demonstrations.

The Light: A powerful green LED shines light into a special plastic rod (like a light pipe) that mixes the light evenly.
The Diamond: This light hits a small diamond sitting on a circuit board.
The Glow: The diamond glows red. A prism (a glass triangle) catches this red glow and sends it to a detector.
The Microwaves: A tiny antenna on the board blasts the diamond with microwaves.
The Magic: When the microwave frequency hits a "sweet spot," the red glow gets dimmer. The computer measures this dimming to calculate the magnetic field.

Why This Matters for Teaching
The authors built this specifically for outreach and teaching labs.

Safety First: Because it uses an LED instead of a laser, students don't need to worry about eye damage or complex safety protocols. They can just turn it on and watch.
See-Through Science: The best part is that you can actually see the magic. The green light and the red glow are bright enough to be seen with the naked eye. Students can watch the red light change right in front of them as they bring a magnet (like a steel screwdriver) near the device.
Real Results: Even though it's simple, it works. The paper shows it can detect magnetic fields with a sensitivity of about 1 microtesla per square root of hertz. To put that in perspective, it's sensitive enough to detect the magnetic field of a nearby paperclip or a steel key, but not sensitive enough to detect the tiny magnetic fields inside a human brain (which requires much more expensive equipment).

The "Cost" of Simplicity
The researchers are honest about the trade-offs.

The Diamond: The most expensive part is still the diamond itself (about $2,000). They chose a high-quality, single crystal diamond because it gives a very clear, sharp signal. If they used cheaper, crushed diamond dust, the signal would be blurry and hard to read, which isn't great for teaching the physics clearly.
The Price Tag: The whole device costs around $4,500. While this is cheaper than a laser-based system, it's not "penny-pinching" cheap. However, the authors argue that for a classroom, the ability to clearly see the signal and the ease of use are worth the cost.

In a Nutshell
This paper presents a "user-friendly" version of a quantum sensor. It takes a complex quantum physics experiment and repackages it into a safe, portable, and visually obvious tool. It allows students and the public to look at a diamond, see it glow, and watch it react to magnets in real-time, making the abstract world of quantum mechanics something you can actually hold and see.

Technical Summary: A Portable LED-Based Diamond Magnetometer for Outreach and Teaching Labs

Problem Statement
The rapid expansion of quantum technology has created a demand for accessible quantum teaching laboratories at the undergraduate level. While Nitrogen-Vacancy (NV) centers in diamond are ideal for demonstrating quantum phenomena such as spin-state dynamics and Zeeman splitting due to their room-temperature stability, standard implementations often rely on complex, expensive, and potentially hazardous equipment. Traditional setups typically utilize green lasers for excitation, necessitating strict laser safety protocols, precise optical alignment, and specialized training. Although recent works have introduced low-cost, modular 3D-printed ODMR (Optically Detected Magnetic Resonance) apparatuses, there remains a need for a system that prioritizes safety, portability, and the direct visual observation of physical processes for public outreach and introductory laboratory settings without requiring laser safety certification.

Methodology
The authors present a compact, portable NV center magnetometer that replaces the standard green laser with a high-power green Light Emitting Diode (LED). The core design utilizes approximately 370 mW of optical power from an LED to excite a millimeter-scale diamond containing a high concentration of NV⁻ centers.

Optical Architecture: The LED output is coupled into a short hexagonal light-mixing rod to homogenize the illumination. This light is directed via a right-angle prism onto the diamond, which is mounted on a printed circuit board (PCB). The same prism collects the resulting red photoluminescence (PL) and directs it back through the mixing rod to a long-pass filter and an amplified photodiode. This geometry eliminates the need for complex lens systems and allows both the green excitation and red fluorescence to be visible to the naked eye.
Microwave and Electronics: The PCB features a printed single-turn loop antenna etched into the top copper layer to generate the oscillating magnetic field required for ODMR. The diamond is positioned directly above this loop for strong near-field coupling. Microwave excitation is supplied by a compact module.
Detection and Control: Signal demodulation is performed using a Red Pitaya STEMLab (a Xilinx Zynq-based FPGA/SoC system) running open-source software to function as a digital lock-in amplifier. A graphical user interface (GUI) allows users to visualize the demodulated ODMR signal in real-time, sweep microwave frequencies, or monitor magnetic field changes at a fixed frequency.
Construction: The device is assembled using off-the-shelf components, including a 3 mm² CVD diamond from Element Six, a Thorlabs LED driver, and a Thorlabs amplified photodetector. The total estimated cost is approximately $4,500, with the diamond representing the most significant expense.

Key Contributions

Safety and Accessibility: By substituting a laser with a high-power LED, the device removes the need for laser safety procedures and complex alignment, making it suitable for environments with minimal supervision, such as public outreach events and undergraduate labs.
Direct Visualization: The design allows students and observers to directly see the green excitation light and the red photoluminescence, providing a tangible link between the physical excitation and the resulting quantum signal.
Portability and Robustness: The entire system packs into two small plastic boxes and can be reassembled in minutes, facilitating transport to different educational venues.
Educational Integration: The authors provide detailed assembly instructions, schematics, Gerber files, and a sample laboratory exercise designed for a 2–3 hour undergraduate session, covering ODMR principles, lock-in detection, and magnetic field estimation.

Results

ODMR Spectroscopy: The device successfully produces clear ODMR spectra. Under a bias magnetic field provided by two permanent block magnets, the system resolves the Zeeman splitting of the NV ground state, showing a pair of resonances corresponding to the $|m_s = 0\rangle \to |m_s = \pm 1\rangle$ transitions.
Magnetometry Performance: The magnetometer demonstrates a sensitivity on the order of $1 \, \mu\text{T}/\sqrt{\text{Hz}}$ . While this is lower than state-of-the-art laser-based systems, it is sufficient for educational demonstrations.
Qualitative and Quantitative Response:
- In qualitative demonstrations, the device responds visibly to nearby magnetic objects; for instance, moving a steel Allen key near the sensor produces a distinct spike in the demodulated photoluminescence signal.
- In quantitative tests using a Helmholtz coil, the lock-in output voltage was shown to vary linearly with the applied coil current, confirming the device's proportionality to magnetic field strength within its operating range.
Operational Modes: The system supports both frequency-swept ODMR spectroscopy and fixed-frequency magnetometry modes, allowing for the investigation of various experimental parameters such as modulation depth, frequency, and LED drive current.

Significance and Claims
The authors claim that this device represents a tailored solution for teaching and outreach environments where the clarity of the fluorescence signal, ease of assembly, and reliability of the demonstration are more critical than achieving the absolute lowest cost or highest sensitivity. While the design does not reach the affordability of some modular, micro-diamond-based options found in literature (which often suffer from broadened spectra due to random crystallite orientations), this design prioritizes spectral clarity and robustness by using a high-quality, single-crystal diamond.

The paper positions the device as a bridge between theoretical quantum concepts and hands-on experimentation, enabling students to visualize spin dynamics and perform basic magnetometry without the barriers of laser safety or complex optical alignment. The authors note that while the diamond constitutes a significant fraction of the total cost, the trade-off is necessary to maintain a clear, interpretable ODMR spectrum suitable for instructional purposes. The work is supported by funding from various UK research councils and foundations, including Innovate UK and the EPSRC.

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