System Bits: Oct. 14

With a combination of solid-state physics and quantum optics, ETH researchers have observed new multiparticle states that could be a first step towards developing photon-based quantum computers; according to MIT researchers, an unexpected finding shows tiny particles keep their internal crystal structure while flexing like droplets, which could have implications for making better nanotechnology components.


Exotic states of light and matter
In research that merges two areas that have only been studied separately, ETH researchers are studying solid-state physics and quantum optics as a potential first step toward quantum computing.

Specifically, the physicists are looking between tiny mirrors to a special layer of the semiconductor material gallium arsenide, prepared in such a way that the electrons can only move within it in two dimensions in the form of 2D electron gas.

They explained that mirrors form a microresonator, which catches photons of a certain wavelength, and that such light cages are standard tools in quantum optics. And with the help of two-dimensional electron gases embedded in a microresonator, the solid-state physicists are studying exotic states of matter. They said they have used techniques from quantum optics to study solid-state systems whose constituents interact strongly with one another.

In previous quantum optics experiments, physicists used intrinsic semiconductors in which a kind of quasiparticle known as an exciton is formed through photon absorption. In a microresonator, the strong interaction with the photons converts these excitons into new quasiparticles representing a mixture of light and matter – these are referred to as polaritons.

However, instead of an intrinsic semiconductor, the team used a 2D electron gas, which, in contrast to conventional 3D semiconductors, the electrons in the 2D gas are not only very mobile but also interact with one another, meaning, they can become strongly correlated.

3D representation of the polariton states of a two-dimensional electron gas in presence of a high magnetic field. (Source: ETH Zurich)

3D representation of the polariton states of a two-dimensional electron gas in presence of a high magnetic field. (Source: ETH Zurich)

The researchers believe this work could make it possible to develop a quantum computer based on interacting photons rather than spin-based or superconducting qubits.

Solid nanoparticles
According to researchers at MIT, a surprising phenomenon has been found in metal nanoparticles in that they appear from the outside to be liquid droplets but their interiors retain a perfectly stable crystal configuration, which could have important implications for the design of components in nanotechnology, such as metal contacts for molecular electronic circuits.

The experiments were conducted at room temperature, with particles of pure silver less than 10nm across, but the results should apply to many different metals.

Silver has a relatively high melting point — 962 degrees Celsius, or 1763 degrees Fahrenheit — so observation of any liquidlike behavior in its nanoparticles was quite unexpected, the researchers said.

The use of nanoparticles in applications ranging from electronics to pharmaceuticals is a lively area of research.

Now that the phenomenon has been understood, researchers working on nanocircuits or other nanodevices can quite easily compensate for it. If the nanoparticles are protected by even a vanishingly thin layer of oxide, the liquidlike behavior is almost completely eliminated, making stable circuits possible.

On the other hand, for some applications this phenomenon might be useful. For example, in circuits where electrical contacts need to withstand rotational reconfiguration, particles designed to maximize this effect might prove useful, using noble metals or a reducing atmosphere, where the formation of an oxide layer is destabilized, the researchers noted.

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