Quantum Computing Update: Dynamic Decoupling and Simultaneous Operations

A team from USC figures out how to improve coherence between quantum states by utilizing accurate bursts of electromagnetic energy, while another team achieved similar results by sending qubits through the same fiber optic cable.

A group of researchers from the University of Southern California have accomplished dynamic decoupling between two quantum states i.e. qubits. Using punctuated bursts of electromagnetic energy they were able to “nudge” both particles in to place gradually as entanglement began to deteriorate, allowing them to stave off any disturbances to computation that would otherwise result.

Using this method they were able to sustain a quantum state up to three times longer than before. The rythmic EM pulses successfully formed a sealed environment around the qubits sequestering them from surrounding perturbations that eventually occur as a result of friction and distance.

As far as this particular strategy is concerned, dynamic decoupling may be more suited for IBMs quantum computer. For example, final coherence between quantum states improved by 59.5% whereas the Rigetti quantum computer yielded an improvement of only 17.3. However, in the end it may depend on how patient Rigetti programmers are and how many pulses they’re willing to use in total. This is because the IBM computer has an upper threshold of 100 pulses before it stops improving whereas the Rigetti quantum computer appears to not possess an upper ceiling at all.

In other news, scientists from the Department of Energys Oak Ridge National Laboratory have discovered how to perform simultaneous operations on several qubits at the same time by sending them through the same fibre optic cable strand.

“To realize universal quantum computing, you need to be able to do different operations on different qubits at the same time, and that’s what we’ve done here,” Lougovski said.

With that being said the quantum operation was performed on an exceedingly small quantum system, the smallest that is – only two. However, it does mark a significant milestone in quantum computation. To be able to perform multiple operations at the same time is, of course, a hallmark for any computational system.

“A lot of researchers are talking about quantum information processing with photons, and even using frequency,” said Lukens. “But no one had thought about sending multiple photons through the same fiber-optic strand, in the same space, and operating on them differently.” “When the photons are taking different paths in the equipment, they experience different phase changes, and that leads to instability,” he said. “When they are traveling through the same device, in this case, the fiber-optic strand, you have better control.”

In order to accomplish the task researchers utilized a quantum frequency processor to invoke a subatomic state called superposition whereby each qubit is entangled in 2 directions at once. By adjusting superposition using electromagnetic impulses scientists are able to program quantum computers – which is the main distinguishing feature between quantum and analog computation.

Afterwards, by sending them through the same fibre optic strand they were able to perform operations on more then one qubit at the same time. In fact researchers demonstrated an interference visibility of 97 percent – which is an indicator of how alike two photons are. Qubits are just another word for the classic informational “bit” instead in this case each “bit” is a quantum entangled photon i.e. “qubit”. In this particular case 97% interference visibility marks a no less then significant improvement over the 70% obtained before.

“We were able to extract more information about the quantum state of our experimental system using Bayesian inference than if we had used more common statistical methods,” Williams said

It would be interesting to study these two strategies in concert with one another to see if we could achieve some kind of synergistic result.

Their research was published in Optica.



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