Measuring a Single Magnetic Moment. New Quantum Chair Launched in Dresden

Overview

Solid-state physicist Aparajita Singha, a leading expert in ultra‑sensitive magnetometry, is pushing the limits of how we detect magnetic fields at the smallest scales. By exploiting atomic defects in diamonds — “NV centers” — she is able to pick up magnetic signatures far too faint for conventional instruments. Singha’s research lays crucial groundwork for future quantum technologies. She has now assumed her professorship in Nanoscale Quantum Materials at the Würzburg–Dresden Cluster of Excellence ctd.qmat — Complexity, Topology and Dynamics in Quantum Matter — and is based at TU Dresden.

Measuring the World’s Smallest Magnet

At the atomic scale, electron spins act like tiny bar magnets whose orientation — up or down — carries information. Traditional semiconductor technologies only process binary information, 0 and 1. By contrast, quantum bits have tremendous quantum power because a spin can exist in a superposition of both states simultaneously. The result is an exponential leap in computational performance — a revolution eagerly pursued worldwide by research laboratories and increasingly by industry.

An expert in magnetometry, Singha measures the magnetic moment of individual atoms using a magnetometer equipped with a diamond‑based quantum sensor. “To read out the information encoded in a spin, you first need to measure it,” she says. “My fascination with quantum sensors began when I wondered whether I could measure the smallest magnet in the world.” That was five years ago, when Singha moved from South Korea to Stuttgart. She has now taken up the chair of Nanoscale Quantum Materials within the Würzburg-Dresden Cluster of Excellence ctd.qmat and has big plans at Technische Universität Dresden: “Over the next five years, my team aims to measure the smallest magnet in the world — at room temperature. No one has done that yet.” 

Diamonds Make It Possible 

At the heart of Singha’s method is a diamond used as a precision quantum sensor. “No diamond is perfect,” she notes. “Natural stones sparkle because of imperfections in their crystal structure. We harness those imperfections and turn them into a powerful tool.“ In the lab, two atomic defects are deliberately engineered into a synthetic diamond. Two carbon atoms are removed from the lattice, then one vacancy is filled with a nitrogen atom while the other is left empty. Together they form an NV center (nitrogen-vacancy center) that responds to tiny magnetic fields. “The light our diamond emits tells us how strong the magnetic moments of our quantum material are,” Singha explains.

The Holy Grail — Sensing at Room Temperature 

For now, detecting the magnetic moment of a single atom still requires extremely low temperatures. Singha expects that to change — she is determined to perform such measurements at room temperature. Achieving this requires refining both the diamond surface (the sensor) and the surrounding experimental environment. “When it comes to the quality of the surface, everything has to be ultra‑clean — as clean as space,” she says. “Only in an ultra‑high vacuum are these amounts of control feasible.”

While quantum materials are typically studied under extreme conditions — near‑absolute‑zero temperatures, intense magnetic fields, and extreme pressures — Singha’s approach is the only technology that currently promises operation at room temperature. “Today we can detect individual atomic spins at 4 K (–269.15°C), and around a hundred spins at room temperature. Our goal is true single‑spin sensitivity under ambient conditions — and that drives our development of new diamond sensors.”

NV Centers — A Global Trend

Being able to observe single spins is vital to both fundamental research and emerging technologies. NV centers are therefore gaining global traction as quantum‑grade sensors. “This worldwide momentum is clearly visible in Saxony. Nearly all regional quantum startups — including several in the new SAX‑QT network — rely on defects in diamonds,” says Matthias Vojta, Dresden spokesperson for the Cluster of Excellence ctd.qmat. “Recruiting a leading expert in this field is a major gain for our research alliance with Würzburg and a boost to the local quantum ecosystem.” 

A New Quantum Professorship for Dresden

Singha studied physics in Kolkata and Mumbai before earning her doctorate in Switzerland. Postdoctoral research led her from Switzerland to South Korea. In 2020, she moved to the Max Planck Institute for Solid State Research in Stuttgart, where she initiated her work with NV centers. Since 2022, she has headed an Emmy Noether independent junior research group on quantum sensing. She formally assumed her ctd.qmat professorship in Dresden on January 1, 2025. This strengthens Dresden's quantum research, which is closely linked to JMU Würzburg (Julius-Maximilians-Universität) through the Cluster of Excellence ctd.qmat. Her team — two postdocs, six doctoral researchers, and a technical specialist — shares a bold objective: to measure the smallest magnet in the world using diamonds and at room temperature.