Mechanical Oscillator Produces Entangled Radiation

Schematic representation of the experiment to produce entangled radiation with a mechanical oscillator. (Source: IST Austria / P. Krantz, Krantz NanoArt)

Physicists from Johannes Fink’s research group at the Institute of Science and Tech­nology Austria (IST Austria) have found a way to use a mechanical oscil­lator to produce entangled radiation. Entangle­ment does not only just affects particles, radiation can also be entangled. This method might prove extremely useful when it comes to connecting quantum computers.

“Imagine a box with two exits. If the exits are entangled, one can charac­terize the radiation coming out of one exit by looking at the other,” postdoc Shabir Barzanjeh explains. Entangled radiation has been created before, but in this study a mechanical object was used for the first time. With a length of 30 micro­meters and composed of about a trillion atoms the silicon beam created by the group might still be small in our eyes but, for the quantum world, however, it is large. “For me, this experiment was interesting on a funda­mental level,” says Barzanjeh. “The question was: can one use such a large system to produce non-classical radiation? Now we know that the answer is: yes.”

But the device also has practical value. Mechanical oscil­lators could serve as a link between the extremely sensitive quantum computers and optical fibers connecting them inside data centers and beyond. “What we have built is a prototype for a quantum link,” says Barzanjeh. In super­conducting quantum computers, the electronics only work at extremely low tempera­tures which are only a few thousandths of a degree above -273.15 °C. This is because such quantum computers operate on the basis of microwave photons which are extremely sensitive to noise and losses. If the tempera­ture in a quantum computer rises, all the information is destroyed. As a conse­quence, transferring infor­mation from one quantum computer to another is at the moment almost impossible, as the infor­mation would have to cross an environment that is too hot for it to survive.

Classical computers in networks, on the other hand, are usually connected via optical fibers, because optical radiation is very robust against distur­bances that could corrupt or destroy data. In order to use this successful technology also for quantum computers, one would have to build a link that can convert the quantum computer’s microwave photons to optical infor­mation carriers or a device that generates entangled microwave-optical fields as a resource for quantum tele­portation. Such a link would serve as a bridge between the room temperature optical and the cryogenic quantum world, and the device developed by the physicists is one step in that direction. “The oscil­lator that we have built has brought us one step closer to a quantum internet,” says Barzanjeh.

But this is not the only potential appli­cation of the device. “Our system could also be used to improve the perfor­mance of gravi­tational wave detectors,” explains Barzanjeh. Johannes Fink adds: “It turns out that observing such steady-state entangled fields implies that the mechanical oscil­lator producing it has to be a quantum object. This holds for any type of mediator and without the need to measuring it directly, so in the future our measurement principle could help to verify or falsify the poten­tially quantum nature of other hard to inter­rogate systems like living organisms or the gravi­tational field.” (Source: IST Austria)

Reference: S. Barzanjeh et al.: Stationary entangled radiation from micromechanical motion, Nature 570, 480 (2019); DOI: 10.1038/s41586-019-1320-2

Link: Quantum Integrated Devices (J. Fink), Physical Sciences, Institute of Science and Technology Austria, Klosterneuburg, Austria

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