April 26, 2013

Transmitting magnetic fields using a superconducting tube designed with transformation optics

A "magnetic hose” consisting of concentric tubes of superconducting and ferromagnetic materials can transmit magnetic fields. A tube consisting of 20 concentric rings that is about ten times longer than it is wide, should transmit about 90 per cent of a magnetic field at one end to the other. Indeed, a tube of just 2 concentric rings should transmit about 75 per cent. Researchers tested the idea with a single superconducting tube 7 cm long (made of BiPbSrCaCuO) and filled with a ferromagnetic alloy (of cobalt and iron).

Exactly how they might build and control these magnetic hoses on this nanometre scale isn’t yet clear. But it’s not beyond the realms of possibility that these devices could become an important enabling technology for quantum information processing in future.

Arxiv - Magnetic hose: Routing and Long-distance Transportation of Magnetic Fields

Magnetism is a fundamental interaction shaping our physical world, at the basis of technologies such as magnetic recording or energy generation. Unlike electromagnetic waves, which can be routed and transmitted with waveguides to long distances, magnetic fields rapidly decay with distance. Here we present the concept, design, and properties of a magnetic hose which enables to transfer the static magnetic fi eld generated by a source to an arbitrary distance, and along any given trajectory. We experimentally demonstrate the fi eld transmission through the simplest hose realization using a superconducting shell with a magnetic core. We discuss possible application of magnetic hoses to harness quantum systems by addressable magnetic fields, in the context of quantum information processing.

The impact of magnetism in science is limited by an apparently insurmountable restriction: magnetic fi elds rapidly decay with the distance from the sources. Our goal in this work is to design a magnetic hose that can route static magnetic fields from their sources (e. g. a magnet) to arbitrary long distances along a desired path, and to come up with a feasible realization. Magnetic fi eld transmission is routinely used in technologies such as transformers, typically using a ferromagnetic (FM) material with high magnetic permeability . However, this only works for small distances, because the transmitted field rapidly decays with distance. Moreover, even though superconductors (SCs) expel magnetic fi eld, they cannot be used to transmit magnetic fi eld lines through a hollow superconductor tube, because the field inside a hollow SC tube decays exponentially. Thus, transmission to arbitrary distances has never been achieved for static fields. A completely di fferent approach is presented in this work. We will proceed in several steps, starting from mathematically exact but unfeasible schemes, based on transformation optics, and ending with feasible proposals that will be experimentally con firmed. Transformation optics allows subwavelength control of electric and magnetic field lines, rather than rays. This has enabled realizing invisibility cloaks, perfect lenses, and waveguides operating in the subwavelength regime. Particularly powerful is the application to static fields like our present case, where one can literally get inside the (in finite) wavelength. We find an exact solution for our goal using transformation optics.

During their experiment, they discovered that this tube was cracked about half way along its length, which allowed any magnetic field it transported to escape.

They placed a coil at one of the tube that generated a magnetic field of 1.3 mTelsa. They then measured the field escaping from the crack as 0.8 mT. That’s significantly higher than the field without the hose. “The magnetic field has been guided through the [superconducting-ferromagnetic] magnetic hose from the coil source up to the crack point, where it escapes to the exterior of the hose,” say Navau and co.

Since we deal with static fields, associated with an infi nite wavelength, these ideas can be implemented at any scale. This hints at the possibility of miniaturizing the magnetic hose to the nanoscale. Such a magnetic nanohose could be used as a new tool to harness quantum systems, as required, for instance, in quantum information processing. In particular, such a device would permit to address, control, and manipulate the internal state of individual quantum systems, even if they are separated by distances of the order of few tens of nanometers, where optical methods are no longer available. This could be particularly relevant in the context of Nitrogen-vacancy (NV) color defect centers in a diamond nanocristal, which have recently been identifi ed as promising systems for the implementation of quantum information processors, or quantum repeaters. So far, we have just considered the transmission of classical magnetic fields. One could also envision a similar system as the one considered here to couple distant quantum systems magnetically, allowing to separate them by relatively long distances and still strongly interact with each other. This would provide us with a very powerful alternative to existing methods that directly couple NV centers at the quantum level. The characterization of such a system, however, requires a full quantum treatment, something that is out of the scope of the present work

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