Improved Method for Interaction-Free Measurements Using Quantum Devices

Improved Method for Interaction-Free Measurements Using Quantum Devices

Vision is typically thought of as the result of light being absorbed by specialized cells in the retina. However, it is also possible for vision to occur without any absorption of light at all, even without a single particle of light being involved.

To understand this concept, consider a camera cartridge that might contain a roll of sensitive film that would be destroyed by exposure to even a single photon. With classical methods, it would be impossible to determine whether there is film in the cartridge, but in the quantum world, this can be done. Anton Zeilinger was the first to experimentally demonstrate this idea using optics.

In a recent study, researchers at Aalto University explored the connection between the quantum and classical worlds and discovered a more effective way to conduct interaction-free experiments. The team used transmon devices, which are superconducting circuits that are large enough to show quantum behavior, to detect the presence of microwave pulses generated by classical instruments. Their findings were published in Nature Communications.

The researchers at Aalto University were interested in the concept demonstrated by Zeilinger’s group, but their lab focuses on microwaves and superconductors rather than lasers and mirrors. To adapt the concept to their available experimental tools, they made a significant change to the standard interaction-free protocol by adding another layer of “quantumness” using a higher energy level of the transmon device and using the quantum coherence of the resulting three-level system as a resource.

Quantum coherence refers to the ability of an object to occupy two different states at the same time, which is possible in quantum physics. However, quantum coherence is delicate and easily collapses, so it was not clear whether the new protocol would work. To the team’s surprise, the first runs of the experiment showed a significant increase in detection efficiency. They ran additional tests and theoretical models to confirm their results and found that the effect was definitely present.

The experiment also demonstrated that even very low-power microwave pulses can be detected efficiently using their protocol and showed a new way in which quantum devices can achieve results that are impossible for classical devices, a phenomenon known as quantum advantage. This is generally thought to require quantum computers with many qubits, but the experiment demonstrated genuine quantum advantage using a relatively simpler setup.

Interaction-free measurements based on the older methodology have already been used in specialized processes such as optical imaging, noise detection, and cryptographic key distribution. The new and improved method developed by the researchers at Aalto University could significantly increase the efficiency of these processes.

The method could also be applied to diagnose microwave-photon states in certain memory elements in quantum computing, providing a highly efficient way to extract information without disturbing the functioning of the quantum processor.

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

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