RRI Develops Non-Invasive Method to Measure Cold Atom Density

Scientists at the Raman Research Institute (RRI), Bengaluru, have developed a novel non-invasive technique to measure the local density of cold atoms in real time without significantly disturbing their quantum state. The breakthrough is expected to accelerate advances in quantum computing, quantum sensing, and high-precision measurement technologies, where accurate control and diagnosis of atomic systems are critical.

Challenges in Cold Atom Measurements

Cold atoms, cooled to temperatures close to absolute zero using laser cooling and trapping, exhibit pronounced quantum behaviour and form the backbone of many emerging quantum technologies. However, accurately measuring their density and quantum state has been a long-standing challenge. Conventional methods such as absorption imaging and fluorescence imaging often disturb or destroy the atomic system. Absorption imaging performs poorly for dense atomic clouds, while fluorescence imaging typically requires long exposure times and alters the atomic state during observation.

Raman Driven Spin Noise Spectroscopy

To overcome these limitations, RRI researchers developed a technique called Raman Driven Spin Noise Spectroscopy (RDSNS). The method builds on spin noise spectroscopy, which detects natural fluctuations in atomic spins via changes in the polarisation of a probe laser. Two additional Raman laser beams coherently drive atoms between neighbouring spin states, amplifying the signal by nearly a million times. This enables precise probing of an extremely small volume of around 0.01 cubic millimetres, targeting regions as small as 38 micrometres containing roughly 10,000 atoms.

Experimental Validation and Key Findings

Using RDSNS, the team studied potassium atoms confined in a magneto-optical trap. They observed that the central density of the atomic cloud saturated within one second, while the total atom number measured through fluorescence imaging took almost twice as long to stabilise. This demonstrates a key advantage of RDSNS: it measures local density rather than only global atom counts. The technique was validated by comparing RDSNS results with fluorescence images processed using the inverse Abel transform, showing close agreement without relying on assumptions of symmetry.

Imporatnt Facts for Exams

• Cold atoms are cooled close to absolute zero using laser cooling techniques.
• Spin noise spectroscopy detects intrinsic fluctuations without strong probing.
• RRI is an autonomous institute under the Department of Science and Technology.
• Non-invasive measurement is crucial for quantum technologies.

Implications for Quantum Technologies

The implications of this development extend across quantum computing and sensing. Real-time, non-destructive density measurements are vital for quantum devices such as gravimeters and magnetometers. According to Prof. Saptarishi Chaudhuri, who leads the QuMIX laboratory at RRI, the technique enables micron-scale probing without disrupting the system, opening new avenues to study quantum transport and non-equilibrium dynamics. Supported under India’s National Quantum Mission, the work positions RRI at the forefront of precision quantum measurement research.