TEKNIK ELEKTRONIKA

that has the property of making objects wrapped in it undetectable to magnetic and very low-frequency electromagnetic fields. The breakthrough brings the dream of "invisibility cloaking" closer to reality and could have important repercussions in both the military and medical fields.

 

Once physically built, the material will make objects "invisible" by annulling the magnetic field residing inside it, but without altering the exterior field. Objects will therefore become impossible to detect through light at these very low frequencies.

 

In order to obtain invisibility, scientists need to manipulate the trajectory of light through the electromagnetic properties of the medium in question. Until no more than a decade ago, scientists thought this to be impossible to achieve; however, recent discoveries have revealed that such manipulation can be possible thanks to the unique properties of a class of exotic materials known as metamaterials.

 

Metamaterials are built by combining two or more materials at the macroscopic level rather than with a chemical process. The one property that makes them particularly attractive is their negative refraction index.

 

When electromagnetic waves such as light are directed at a transparent object, part of the beam is reflected by the object, while the remaining part propagates within it. The direction of the beam that enters is modified by an angle that depends on the object's refraction index. While the vast majority of objects found in nature have a positive refraction index, its value for metamaterials is negative, which allows to bend light and other electromagnetic waves in a very different way, making invisibility possible.

 

The team's theoretical work brought to the design of a metamaterial consisting in an irregular network of superconductors, which give them specific magnetic properties that can create invisible areas in the magnetic field and in very low frequency electromagnetic fields.

 

Invisibility in visible light has not yet been achieved with experiments, but scientists are working with other types of light such as microwaves, low frequency electromagnetic fields such as radio or television waves, and even with the Earth's magnetic field.

 

Possible applications

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Scientists at the Delft University of Technology (Netherlands) and the Ames Laboratory of the US Department of Energy have managed to fully protect the spin state of a single electron from its environment. Single solid state spins are promising building blocks for new quantum technologies, such as quantum computers, but uncontrolled interactions between spins and their environment have been a major obstacle. By repeatedly flipping the spin of a single electron with very short pulses, the researchers were able to mitigate these effects, effectively decoupling the spin from its environment. They also showed that the technique works with any possible spin state, a stringent requirement for use in a future quantum computer.
The researchers worked with single electrons in diamond, a material that has recently become very popular with quantum scientists. Diamonds have the unique property that quantum mechanical effects can be seen even at room temperature, which is a major advantage for future applications. Previously the researchers were able to measure the spin state of a single electron in diamond and probe its environment. Now, using high-frequency pulses only a few nanoseconds long, the team has achieved control over the state of a single spin with unprecedented accuracy. They have exploited this control to protect the spin from its environment, a groundbreaking result.

The researchers periodically rotated the spin with very high precision so that the environmental effects were fully cancelled by averaging. This caused the spin to be virtually decoupled from its environment. The more often they flipped the spin, the longer its quantum state was preserved. With 130 pulses, the duration of the spin state was 25 times longer than previously measured. In addition, they demonstrated that the protection is effective for any arbitrary spin state.

These results are a true breakthrough for quantum science and engineering, where uncontrolled interactions with the environment have up to now been a major obstacle to new basic research and applications.

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