System Bits: March 10

Surviving entanglement breakdown; snake states; graphene’s thermal conductivity.

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Surviving entanglement breakdown
Researchers at MIT have discovered that preserving the fragile quantum property known as entanglement isn’t necessary to reap benefits.

By way of background, the MIT team reminded that the promise of quantum information processing, i.e., solving problems that classical computers can’t, as well as perfectly secure communication depends on a phenomenon called entanglement whereby the physical states of different quantum particles become interrelated. However, entanglement is very fragile, therefore the difficulty of preserving it is a major obstacle to developing practical quantum information systems.

For the past five years, members of the Optical and Quantum Communications Group at MIT’s Research Laboratory of Electronics have postulated that optical systems using entangled light can outperform classical optical systems even when the entanglement breaks down.

Not only that but two years ago, they demonstrated that systems that begin with entangled light could allow a more efficient means of securing optical communications. Now, they’ve demonstrated that entanglement can also improve the performance of optical sensors, even when it doesn’t survive light’s interaction with the environment.

In the researchers' new system, a returning beam of light is mixed with a locally stored beam, and the correlation of their phase, or period of oscillation, helps remove noise caused by interactions with the environment. (Source: MIT)

In the researchers’ new system, a returning beam of light is mixed with a locally stored beam, and the correlation of their phase, or period of oscillation, helps remove noise caused by interactions with the environment.
(Source: MIT)

MIT senior research scientist Franco Wong said this is something that’s been missing in the understanding that many in the field hold — that if unavoidable loss and noise make the light being measured look completely classical, then there isn’t a benefit to starting out with something quantum, since they think it can’t help. This research shows that it does help.

This technology could be a stepping stone towards the development of a quantum LIDAR which is able to spot almost-invisible objects in a very noisy background. Also, the working mechanism of quantum illumination could be exploited at short distances to develop, for example, non-invasive techniques of quantum sensing with potential applications in biomedicine.

Graphene electrons moving along predefined snake states
Potentially providing a basis for a number of electronics applications, physicists at the University of Basel have shown for the first time that electrons in graphene can be moved along a predefined path, which occurs entirely without loss.

Researchers at the University of Basel have developed methods that allow them to stretch, examine and manipulate layers of pure graphene, and have discovered that electrons can move in this pure graphene practically undisturbed – similar to rays of light. To lead the electrons from one specific place to another, they planned to actively guide the electrons along a predefined path in the material.

For the first time, the scientists succeeded in switching the guidance of the electrons on and off and guiding them without any loss by applying a mechanism applied that is based on a property that occurs only in graphene.

The principle of the experiment: The honeycomb grid provides an atomic graphene layer stretched between two electrical contacts (silver). The lower area contains two control electrodes (gold), which are used to generate an electrical field. A magnetic field is also applied vertically to the graphene level. Combining an electrical field and a magnetic field means that the electrons move along a snake state. (Source: University of Basel)

The principle of the experiment: The honeycomb grid provides an atomic graphene layer stretched between two electrical contacts (silver). The lower area contains two control electrodes (gold), which are used to generate an electrical field. A magnetic field is also applied vertically to the graphene level. Combining an electrical field and a magnetic field means that the electrons move along a snake state. (Source: University of Basel)

Combining an electrical field and a magnetic field means that the electrons move along a snake state. The line bends to the right, then to the left. This switch is due to the sequence of positive and negative mass – a phenomenon that can only be realized in graphene and could be used as a novel switch, operated by altering the magnetic field or the electrical field.

Graphene’s thermal conductivity
Providing key information for engineering future electronics, EPFL researchers have shed new light on the fundamental mechanisms of heat dissipation in graphene and other 2D materials, showing that heat can propagate as a wave over very long distances.

As electronics get smaller and faster, new methods are needed to improve the cooling. One idea is to use materials with very high thermal conductivity — such as graphene — to quickly dissipate heat and cool down the circuits.

An outstanding questions in the industry has been how heat propagates inside these sheets of materials that are no more than a few atoms thick.

To this end, the EPFL team has demonstrated that heat propagates in the form of a wave, just like sound in air. Until now this was a very obscure phenomenon observed in few cases at temperatures close to the absolute zero.Their simulations provide a valuable tool for researchers studying graphene, whether to cool down circuits at the nanoscale, or to replace silicon in tomorrow’s electronics.

The work shows that heat can propagate without significant losses in 2D even at room temperature, thanks to the phenomenon of wave-like diffusion, called second sound.



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