Researchers use quantum mechanics to see objects without looking at them

Researchers use quantum mechanics to see objects without looking at them

Quantum researchers at Aalto University use quantum coherence to detect objects without looking at them. Credit: Mikko Raskinen/Aalto University

We see the world around us because light is being absorbed by specialized cells in our retina. But can vision occur without any kind of absorption, without even a single particle of light? Surprisingly, the answer is yes.

Imagine that you have a camera cartridge that can hold a roll of photographic film. The scroll is so sensitive that contact with a single photon would destroy it. With our classic everyday media, there is no way to tell if there is film in the cartridge, but in the quantum world Can be done. Anton Zeilinger, one of the winners of the 2022 Nobel Prize in Physics, was the first to experimentally implement the idea of ​​an interaction-free experiment using optics.

Now, in a study exploring the connection between the quantum and classical worlds, Shruti Dogra, John J. McCord, and Gheorghe Sorin Paraoanu of Aalto University have discovered a new and much more effective way to carry out experiments without interaction. The team used transmon devices (superconducting circuits that are relatively large but still exhibit quantum behavior) to detect the presence of microwave pulses generated by classical instruments. Their research was recently published in nature communications.

An experiment with an extra layer of ‘quantification’

Although Dogra and Paraoanu were fascinated by the work done by Zeilinger’s research group, their lab focuses on microwaves and superconductors rather than lasers and mirrors. “We had to adapt the concept to the different experimental tools available for superconducting devices. Because of that, we also had to change the interaction-free standard protocol in one crucial way: we added another ‘quantum’ layer by using a higher energy level. of the transmon. Then we use the quantum coherence of the resulting three-level system as a resource,” says Paraoanu.

Quantum coherence refers to the possibility that an object can occupy two different states at the same time, something that quantum physics allows for. However, quantum coherence it’s delicate and collapses easily, so it wasn’t immediately obvious that the new protocol would work. To the pleasant surprise of the team, the first few runs of the experiment showed a marked increase in detection efficiency. They went back to the drawing board several times, ran theoretical models that confirmed their results, and double-checked everything. The effect was definitely there.

“We also show that even very low-power microwave pulses can be efficiently detected using our protocol,” says Dogra.

The experiment also showed a new way that quantum devices can achieve results that are impossible for classical devices, a phenomenon known as quantum advantage. Researchers generally believe that achieving quantum advantage will require quantum computers with many qubits, but this experiment demonstrated genuine quantum advantage using a relatively simpler setup.

Potential applications in many types of quantum technology

Non-interaction measurements based on the earlier, less effective methodology have already found applications in specialized processes such as optical imaging, noise detection, and cryptographic key distribution. The new and improved method could dramatically increase the efficiency of these processes.

“In quantum computing, our method could be applied to diagnose microwave photon states in certain memory elements. This can be considered a very efficient way of extracting information without disturbing the operation of the quantum processor,” says Paraoanu.

The Paraoanu-led group is also exploring other exotic forms of information processing using their new approach, such as counterfactual communication (communication between two parties without any physical particles being transferred) and counterfactual communication. quantum computing (where the result of a calculation is obtained without running the computer).

More information:
Shruti Dogra et al, Non-interacting coherent detection of microwave pulses with a superconducting circuit, nature communications (2022). DOI: 10.1038/s41467-022-35049-z

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Aalto University

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