- Why in news
- On 24 September 2026, the Ministry of Science & Technology reported that Raman Research Institute (RRI) researchers made the first experimental measurement of a quantum measure above one (about 1.17), published in the journal Quantum.
- What it is
- Quantum Measure Theory (QMT) describes a quantum system through its possible histories, not just its state at one time. It assigns a generalized measure to sets of histories, including interference between them. Unlike ordinary probability, this measure can exceed one.
- Who did it
- The experiment was done at the Raman Research Institute, an autonomous institute of the Department of Science and Technology.
- The result
- The measured quantum measure was about 1.17, close to the predicted value of about 1.18 after allowing for apparatus imperfections.
- Method
- An 'event-filter' used polarisation to tell photon routes apart and select a chosen set. The distinguishing information was then erased so the routes could interfere.
- Key caveat
- No probability above one was measured. The detector probability stays below one; only the quantum measure exceeds one.
- Quantum gravity link
- QMT was developed partly by Rafael Sorkin in the search for quantum gravity. This experiment does not test a theory of quantum gravity.
- Polarisation
- Polarisation is the orientation in which light waves oscillate.
Don’t confuse with Quantum measure vs probability: The quantum measure includes interference between histories and can exceed one. The detection probability is an ordinary probability and stays between 0 and 1.
Don’t confuse with Experiment vs test of quantum gravity: The experiment makes QMT measurable in the lab. It does not test or confirm any theory of quantum gravity.
Science and technology: 57 Prelims questions since 2013; most test the concept behind the news, not the news itself. In Mains, 12 news-triggered questions.
Why it matters
- Shows an abstract quantity in quantum foundations can be measured in a lab.
- Event-filtering could become a tool for quantum measurement and quantum computing.
Problems
- Current setup is not yet a practical tool; the release speaks only of a future implementation.
- It does not resolve the quantum measurement problem.
Way forward
- Build event-filters that select photon paths while leaving photons usable for further quantum operations.
Put in your answer
Indian quantum research example: The RRI team led by Urbasi Sinha performed the first measurement of a quantum measure exceeding one, showing Indian institutes' role in quantum foundations.
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No practice question for this one; the card may still help an answer. Why: Lasting science topic from an Indian institute (RRI), but too specialised; UPSC sci-tech questions favour concepts, 57 of 327 in Prelims.
Worth revising until Prelims 2028: most news questions come within two years of the event.