Scientists develop new way to tackle key quantum computing challenge - The Indian Express

Scientists at the Quantum Information and Computing (QuIC) laboratory at Raman Research Institute in Bengaluru have demonstrated a novel way to increase the stability of the quantum states that enable computation in a quantum computer that can potentially improve the reliability and integrity of these calculations.

Unlike traditional computers that encode electric states into 0s and 1s to store and process information, quantum computers make use of the very unique, but counter-intuitive, properties of the quantum world to carry out calculations.

One of these happens to be “quantum entanglement,” a remarkable property of the quantum world in which two particles, after undergoing an interaction, get “linked” (or entangled) together in such a way that they begin to behave like one single system. Measuring certain properties of one reveals information about corresponding properties of the other, irrespective of the distance between the two.

Scientists have used this, along with some other special properties like superposition — the ability of quantum particles to exist in multiple states at the same time — to build powerful quantum computers which can perform certain very complex computations in an efficient manner.

But the quantum states that give superpowers to these computers are themselves very fragile and ephemeral. The entangled state, for example, disintegrates very quickly on interaction with the external environment, a phenomenon known as decoherence. Sometimes, entanglement vanishes abruptly, too, even before the normal disintegration takes place. Scientists call this condition “entanglement sudden death.”

This weakness creates a problem for quantum computing. The integrity of the calculations becomes doubtful. Scientists have tried to deal with this challenge by carrying out repeated corrective interventions that delay decoherence. But these repetitive interventions have their own side-effects. They are costly, and can introduce errors of their own.

This is where the research team of Urbasi Sinha, group leader of the lab at RRI, has achieved a breakthrough. Instead of repetitive operations, her team has developed a new technique that deals with decoherence in this context through a “single-shot operation.”

Depending on the instant when the operation is carried out, this operation can delay decoherence and entirely avoid sudden death.

Applied at some other instant, this operation can even hasten decoherence, though it is not an outcome that is scientifically desirable. This operation, therefore, gives scientists greater control over the different possibilities.

“To me, the heart of the result is that that the timing of the operation is not just an experimental detail, it can be a control resource,” said Sinha, a senior professor at RRI. She said her experiments presented a proof of concept, something that has relevance to the problem of decoherence, rather than a complete solution. It would need to be tested out by different quantum computing systems to see how advantageously it can be applied in different environments.

The results of experiments by Sinha’s team has been published in a paper in the American Physical Society’s Physical Review A.

“We are not claiming to have solved decoherence or replaced quantum error correction, rather the work identifies timing itself as another control parameter that future quantum processors could exploit alongside better materials, better gates, and error-correction protocols,” she said.

“Our experiment shows that one does not always have to fight decoherence with long sequences of corrective operations. The timing of a single local gate can redirect the entanglement trajectory and extend the regime over which the state remains useful,” she said.