RRI scientists show a well-timed single operation can delay quantum decoherence
Entangled particles lose their link in a flash. Can one well-timed flip keep it alive longer?
Published 15 September 2026. Written by Pratidin from the reports linked at the end; every fact checked by a separate review before publishing. How we work
Scientists at the Quantum Information and Computing (QuIC) laboratory of the Raman Research Institute (RRI), Bengaluru, led by Urbasi Sinha, have developed a 'single-shot' technique to tackle decoherence, one of the central obstacles to building quantum computers, The Indian Express reported on its front page on 15 September 2026. The results were published in the American Physical Society's journal Physical Review A. The method applies a single 'flip' operation to an entangled quantum system. Depending on when the flip is applied, it can delay decoherence and, in some cases, entirely avoid 'entanglement sudden death', the abrupt loss of entanglement. The study suggests that the timing of an operation can itself be used as a tool to control quantum states.
Quantum computers rely on two properties that ordinary computers do not use. Superposition lets a quantum particle exist in more than one state at once until it is measured. Entanglement links two particles after they interact, so that they behave as a single system, and measuring one reveals information about the other however far apart they are. Both are fragile. When a quantum system interacts with its surroundings, its quantum character leaks away, a process called decoherence. Entanglement can also vanish suddenly, well before normal decay would have removed it. Existing strategies against decoherence often need repeated corrective interventions, which add cost and create more chances for error, alongside better materials, better gates and error correction.
RRI was founded by C.V. Raman in 1948 and has been an autonomous institute funded by the Department of Science and Technology since 1972. In February 2021 a team under Urbasi Sinha demonstrated free-space quantum key distribution between two buildings 50 metres apart. The new work fits into the National Quantum Mission, approved by the Union Cabinet on 19 April 2023 with an outlay of ₹6,003.65 crore for 2023-24 to 2030-31. The Mission aims to develop intermediate-scale quantum computers with 50 to 1,000 physical qubits in eight years and inter-city quantum key distribution over 2,000 km, through four thematic hubs on quantum computing, quantum communication, quantum sensing and metrology, and quantum materials and devices.
Prelims facts
- RRI Bengaluru's QuIC laboratory, led by Urbasi Sinha, showed that a single, well-timed flip operation can delay decoherence and in some cases avoid entanglement sudden death; the work was published in Physical Review A.
- Decoherence is the loss of a system's quantum behaviour through interaction with its environment.
- Entanglement sudden death is the abrupt disappearance of entanglement before normal decay would remove it.
- National Quantum Mission: approved 19 April 2023, ₹6,003.65 crore for 2023-24 to 2030-31, targeting quantum computers with 50 to 1,000 physical qubits in eight years.
- RRI was founded by C.V. Raman in 1948 and is an autonomous institute funded by the Department of Science and Technology.
Quick recall
- Which RRI laboratory produced the single-shot decoherence result, and who leads it?
- The Quantum Information and Computing (QuIC) laboratory, led by Urbasi Sinha.
- In which journal was the RRI decoherence work published?
- Physical Review A, of the American Physical Society.
- What is decoherence?
- Loss of a system's quantum behaviour through interaction with its environment.
- What is entanglement sudden death?
- The abrupt vanishing of entanglement in a finite time, before normal decay would remove it.
- What single operation did RRI use to delay decoherence?
- A 'flip' operation, whose effect depends on when it is applied.
- Outlay and period of the National Quantum Mission?
- ₹6,003.65 crore, 2023-24 to 2030-31 (approved 19 April 2023).
- What quantum computer target does the National Quantum Mission set?
- Intermediate-scale computers with 50 to 1,000 physical qubits in eight years.
- Who founded the Raman Research Institute, and when?
- C.V. Raman, in 1948.
Prelims practice question
With reference to quantum technology, consider the following statements:
1. Decoherence is the loss of the quantum properties of a system due to its interaction with the environment.
2. 'Entanglement sudden death' refers to the slow, gradual decay of entanglement over a very long time.
3. The National Quantum Mission targets intermediate-scale quantum computers with 50 to 1,000 physical qubits in eight years.
How many of the statements given above are correct?
- Only one
- Only two
- All three
- None
Show answer
Answer: (b) Only two. Statement 1 is correct. Statement 2 is incorrect: entanglement sudden death is the abrupt vanishing of entanglement in a finite time, before normal decay would remove it. Statement 3 is correct: the Mission, approved on 19 April 2023, targets 50 to 1,000 physical qubits in eight years.
Use this in UPSC Mains: previous-year questions
Recurring theme: Indigenous research in frontier technologies
- How to use this
The RRI result is a counter-example showing frontier research continuing in Indian institutes, backed by mission-mode funding under the National Quantum Mission.
- RRI Bengaluru's QuIC laboratory, led by Urbasi Sinha, showed in Physical Review A that a single well-timed flip can delay decoherence and sometimes avoid entanglement sudden death.
- The same team demonstrated free-space quantum key distribution between two buildings 50 metres apart in February 2021.
- The National Quantum Mission (approved 19 April 2023, ₹6,003.65 crore for 2023-24 to 2030-31) funds four thematic hubs and targets 50 to 1,000 physical qubit computers in eight years.
Quantum communication and computing under the National Quantum Mission are the next frontier after space technology in India's science and technology achievements.
Mains practice question
What is decoherence, and why is it the central hurdle in building quantum computers? Discuss India's efforts under the National Quantum Mission. (150 words)
Model answer
Decoherence is the loss of a quantum system's superposition and entanglement when it interacts with its environment. It limits how long qubits can hold information.
Why it is the central hurdle
- Qubits must stay coherent through a whole computation; heat and stray disturbances cut that time short.
- Entanglement can collapse abruptly ('entanglement sudden death').
- Repeated corrective steps add cost and fresh errors.
Recent Indian research
- RRI Bengaluru's QuIC laboratory (Physical Review A) showed that one well-timed flip can delay decoherence and sometimes avoid sudden death.
National Quantum Mission
- Approved 19 April 2023; ₹6,003.65 crore for 2023-24 to 2030-31.
- Targets 50 to 1,000 physical qubit computers in eight years and inter-city quantum key distribution over 2,000 km.
- Four thematic hubs: computing, communication, sensing and metrology, materials and devices.
Solving decoherence, through timing, materials and error correction, will decide whether these targets are met.
The basics
Why this matters
Quantum computers promise to solve some problems that ordinary computers cannot, but their building blocks are extremely fragile. The central engineering problem is keeping quantum states alive long enough to compute with them. A result from the Raman Research Institute (RRI), Bengaluru, reported on the front page of The Indian Express on 15 September 2026, offers a new, simple tool for that problem: timing.
Bits and qubits
An ordinary computer stores information in bits that are either 0 or 1. A quantum computer uses Qubits and superposition: a qubit can be in a combination of 0 and 1 at the same time until it is measured. Qubits can also be linked through Quantum entanglement, so that two particles behave as one system even when far apart.
- Either 0 or 1 at any moment
- Reading it does not change it
- Robust against small disturbances
- Can be in a superposition of 0 and 1
- Measurement forces it into one outcome
- Loses its quantum character through contact with the environment
The enemy: decoherence
When a quantum system interacts with its surroundings, its quantum behaviour leaks away. This is Decoherence and entanglement sudden death. Entanglement can even vanish abruptly, well before ordinary decay would have removed it. Existing fixes apply repeated corrective interventions, which add cost and create more chances for error.
- 1Two particles are entangled and behave as one system
- 2The system interacts with its environment
- 3Quantum correlations leak away into the surroundings
- 4Entanglement fades, or dies suddenly, and must be prepared again
The RRI idea
The QuIC laboratory at RRI, led by Urbasi Sinha, showed that a single 'flip' operation, applied at the right moment, can delay decoherence and in some cases avoid entanglement sudden death altogether. The results appeared in Physical Review A. The key variable is when the flip is applied, which makes timing a control tool alongside better materials, better gates and error correction.
- 1EntanglePrepare an entangled pair of quantum particles
- 2Let it evolveThe pair begins to lose entanglement through contact with its environment
- 3Flip onceApply one flip operation at a chosen time
- 4CompareDepending on timing, decoherence is delayed or sudden death is avoided
The national frame
Work like this feeds the National Quantum Mission, approved in April 2023 with ₹6,003.65 crore for 2023-24 to 2030-31.
Go deeper
In one line: Scientists at the Raman Research Institute, Bengaluru, have shown that applying a single 'flip' operation at the right time can delay decoherence and, in some cases, prevent the sudden death of quantum entanglement.
Why it matters for UPSC
Quantum technology is a priority area under the National Quantum Mission and a recurring theme in GS3 questions on science and technology and indigenous research. Prelims can test basic terms such as qubit, superposition, entanglement and decoherence, and the Mission's outlay and targets.
The core idea
Quantum computers work with Qubits and superposition and use Quantum entanglement to link qubits. Both are destroyed by Decoherence and entanglement sudden death, which happens when a quantum system interacts with its environment. The usual answer is repeated correction, which is costly and error-prone. The RRI team, led by Urbasi Sinha at the Quantum Information and Computing (QuIC) laboratory, found that one well-timed flip can do much of the job, making timing itself a control tool. The work sits within India's National Quantum Mission.
Numbers and dates to remember
- Journal: Physical Review A (American Physical Society).
- 1948: RRI founded by C.V. Raman; autonomous institute funded by the Department of Science and Technology since 1972.
- February 2021: RRI team under Urbasi Sinha demonstrates free-space quantum key distribution between buildings 50 metres apart.
- 19 April 2023: Cabinet approves the National Quantum Mission.
- ₹6,003.65 crore, 2023-24 to 2030-31: the Mission's outlay and period.
- 50 to 1,000 physical qubits in eight years; inter-city quantum key distribution over 2,000 km.
Where to go next
- Qubits and superposition: what makes a quantum bit different.
- Quantum entanglement: the link between particles that quantum technology relies on.
- Decoherence and entanglement sudden death: why quantum states fall apart.
- National Quantum Mission: India's plan, money and targets.
Go deeper: how to keep a quantum state alive
The problem. A quantum computer is only useful while its qubits stay coherent. Every interaction with the outside world, such as heat, stray fields or vibrations, carries away some of the quantum information. This is Decoherence and entanglement sudden death. For entangled qubits the loss can be abrupt: entanglement can drop to zero in a finite time, not just fade slowly.
The usual toolkit. Engineers attack decoherence on several fronts: better materials that interact less with qubits, better gates (the operations that change qubit states), and error-correction methods that spread one logical qubit across many physical ones and repair errors. Many strategies also apply repeated corrective interventions during a computation. Each extra intervention costs time and resources and is itself a chance to introduce error.
What RRI adds. The QuIC team's approach is 'single-shot': one flip operation, not a series. Its effect depends on when it is applied. Chosen well, it delays decoherence and can avoid entanglement sudden death entirely. The finding treats timing as a control knob that complements, rather than replaces, materials, gates and error correction. The same laboratory had earlier demonstrated free-space quantum key distribution, in 2021.
Why India cares. The National Quantum Mission aims for intermediate-scale quantum computers with 50 to 1,000 physical qubits in eight years. Getting there depends on keeping Qubits and superposition and Quantum entanglement stable long enough to compute, which is exactly what research on decoherence control addresses.
Qubits and superposition
What makes a quantum bit different from a classical one.
In one line: A qubit is the basic unit of quantum information; unlike a classical bit, it can exist in a superposition of 0 and 1 until it is measured.
Superposition from zero
A classical bit is a switch: off (0) or on (1). A qubit can be in a blend of both states at once, described by probabilities for each outcome. When it is measured, it gives either 0 or 1, and the superposition is lost. Qubits can be made from different physical systems, such as photons (particles of light), trapped ions or tiny superconducting circuits.
Why it matters
Because many qubits in superposition can represent many combinations at once, quantum computers can in principle handle certain problems far faster than classical machines. But superposition is delicate. Contact with the environment destroys it, which is why the RRI work on delaying decoherence matters.
Where to go next
Quantum entanglement
The link between particles that quantum technology relies on.
In one line: Entanglement is a link between two or more particles, created when they interact, that makes them behave as a single system however far apart they are.
How it works
When two particles are entangled, measuring a property of one immediately tells you about the matching property of the other. This correlation holds even if the particles are separated by large distances. It cannot be explained by ordinary, classical links between objects.
Why it is useful
Entanglement is a resource for quantum computing, where it links qubits so they can work together, and for quantum communication. Quantum key distribution, for example, uses quantum states to share encryption keys in a way that reveals any eavesdropping. RRI's QuIC laboratory demonstrated free-space quantum key distribution between two buildings 50 metres apart in February 2021. The weakness is that entanglement is easily destroyed by the environment.
Where to go next
Decoherence and entanglement sudden death
Why quantum states fall apart, and what RRI's method changes.
In one line: Decoherence is the loss of a system's quantum behaviour through interaction with its environment; entanglement sudden death is the abrupt vanishing of entanglement before normal decay would remove it.
Decoherence
A perfectly isolated quantum system keeps its superposition and entanglement. Real systems are never perfectly isolated. Heat, light and other disturbances interact with the qubits and carry quantum information away, so the system starts to behave like an ordinary, classical one. This sets a time limit on any quantum computation.
Entanglement sudden death
One might expect entanglement to fade gradually. Instead, it can drop to zero in a finite time. Physicists call this entanglement sudden death. The RRI team showed that a single flip operation, applied at the right moment, can delay decoherence and in some cases avoid sudden death entirely. Existing methods rely on repeated corrective steps, which add cost and error.
Where to go next
National Quantum Mission
India's plan, money and targets for quantum technology.
In one line: The National Quantum Mission, approved by the Union Cabinet on 19 April 2023, aims to build Indian capability in quantum technologies with an outlay of ₹6,003.65 crore from 2023-24 to 2030-31.
Targets
- Intermediate-scale quantum computers with 50 to 1,000 physical qubits in eight years.
- Inter-city quantum key distribution over 2,000 km within India.
- Work across four thematic hubs: quantum computing, quantum communication, quantum sensing and metrology, and quantum materials and devices.
Why it is in the news
Research such as RRI's single-shot control of decoherence addresses the main barrier to the Mission's computing goals: keeping qubits coherent long enough to be useful. RRI, founded by C.V. Raman in 1948, is an autonomous institute funded by the Department of Science and Technology.
Where to go next
National Quantum Mission: every story that connects to it (2)
Take the 15 September 2026 quiz: 30 Prelims-style questions with answers