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qubit states

Researchers discover superconductor that could enhance quantum computer development

Scientists at the National Institute of Standards and Technology (NIST) have discovered a superconductor that could very probably be useful for developing quantum computers by overcoming one of the main barriers in the development of effective quantum logic circuit. The paper has been published in Science journal.

Recently unearthed properties in the compound uranium ditelluride or UTe2 show that it could be highly resilient to one of the nemeses of quantum computer development – the problem with making memory storage switches of a quantum computer known as qubits, to function long enough to complete a calculation before losing the sensitive physical relationship that allows them to function as a group. This is known as quantum coherence which is difficult to sustain because of disturbances from the surrounding world.

It is one of the rare superconductor materials because of its peculiar and strong resistance to the magnetic field and provides benefits for qubit design, mainly their resistance to the fallacies that can easily drag into the quantum calculation. The research team’s Nick Butch said that UTe2’s unique properties could make it alluring to the emerging quantum computer sector.

Butch, a physicist at the NIST Center for Neutron Research (NCNR) said that uranium ditelluride which is the silicon of the quantum information era could be used to build the qubits of an efficient quantum computer.

Results of research team which includes scientists from Ames Laboratory and the University of Maryland explain UTe2’s exceptional characteristics, interesting from viewpoint of both technical application and fundamental science.

Electrons that conduct electricity travel as separate particles in copper wire or some other ordinary conductor but in Superconductors, they form cooper pairs and the electromagnetic interactions that produce these pairings are responsible for the material’s superconductivity. BCS theory which explains this type of superconductivity is named after the three scientists who revealed the pairings and also won the Nobel prize for that.

The property of electrons that is especially important to the cooper pairing is the quantum “spin” that makes electrons act as if they have a little bar magnet running through them. In the majority of superconductors, the paired electrons have their quantum spins oriented one upward and other downwards and the opposed pairing is called a spin-singlet.

The Cooper pairs in UTe2 can have their spins oriented in one of three combinations making their spin triplets oriented in parallel rather than opposition making it nonconformists like the very few known superconductors. Most of the spin-triplet SCs are assumed to be “topological” with an extremely useful quality in which the superconductivity occurs on the material’s surface and persist even in the presence of outer shocks.

These parallel spin pairs could help the computer keep operative and can’t automatically collapse because of quantum variations. Superconductor has been perceived to have advantages as the basis for quantum computer elements, and recent economical advances in quantum computer development have engaged circuits made from superconductors, unlike the quantum computer that need a way to correct the errors that drag in from their surroundings because of the topological SC’s properties.

Butch said that Topological superconductors are a substitute path to quantum computing because of long lifespan and it gives error-free qubits and also protects it from the environment.

Researchers stumbled upon UTe2 while exploring uranium-based magnets whose electronic properties can be adjusted as desired by changing their chemistry, pressure or magnetic field and is a useful feature for customizable materials (the material consists of slightly radioactive “depleted uranium”).

UTe2 was first developed back in the 1970s but recently while making some UTe2 while they were synthesizing related materials, they experimented it at lower temperatures to see if any event might have been ignored and they noticed that they had something very special.

The NIST team at both the NCNR and the University of Maryland started studying UTe2 with specialized tools and noticed that it became superconducting at low temperatures (below -271.5 oCelsius, or 1.6 Kelvin) with properties resembling rare ferromagnetic superconductors which acts like low-temperature permanent magnets. Yet, strangely UTe2 is itself not ferromagnetic which makes it fundamentally new.

UTe2 can resist fields as high as 35 Tesla which is 3,500 times strong as a normal refrigerator magnet, and much more than the lowest temperature topological SCs can resist.

This extraordinary resistance to strong magnetic fields means it is a spin-triplet SC and likely a topological SC as well and will help researchers to study the nature of UTe2 and superconductivity itself. The main purpose of this research and exploring SC’s is to study superconductivity and to know where to look for undiscovered SC materials which is difficult right now and also to understand what stabilizes these parallel-spin SCs.

Journal Reference: Science journal

Quantum Refrigerator

Scientists create superconducting quantum refrigerator

Imagine if we can think of a refrigerator so cold that it could turn atoms into their quantum states giving those properties that defy classical physics rules. In a paper published in Physical Review Applied, Andrew Jordan, physics professor at University of Rochester, and graduate student Sreenath Manikandan, along with other scientists put forward an idea that would cool atoms to nearly absolute zero temperatures and would be based on the quantum property of superconductivity which can be used to enhance the performance of quantum sensors for ultrafast computing.

The ability of a metal to conduct electricity is called conductivity. A metal with high conductivity allows electric current to flow through and offers negligible resistance to the flow of electrons. A superconductor is a scenario where the material would conduct electricity without encountering resistance and current would circulate indefinitely without any resistance. When you cool down electrons to extreme temperatures, electrons flow like a fluid without resistance. This is possible due to Cooper Pair formation at low temperatures. When you reach such low temperature, the resistance abruptly drops to zero and there is a phase transition that occurs.

Researchers could then change material into a superconducting state which is similar to material in solid, liquid or gaseous state. The operating principles of these refrigerators are quite similar to that of traditional refrigerators as both use a phase transition to get the cooling power required.

A conventional refrigerator is usually hot on the backside and operates by removing inside heat by moving a fluid called refrigerant between hot and cold reservoirs by changing the state from liquid to gas. The refrigerant in liquid form passes through expansion valve due to which there is a drop in pressure and temperature due to gaseous form. It passes through the coils absorbing heat from the system. It is again compressed into liquid by the compressor and radiating absorbed heat and the cycle is repeated however in a superconducting refrigerator instead of using a refrigerant, the electrons in the metal changes from the paired superconducting state to an unpaired normal state.

In a superconducting quantum fridge, researchers placed a layered stack of metals in a cold dilution refrigerator. The bottom layer is a sheet of superconducting niobium, the middle layer is the superconductor tantalum and the top layer is copper.

Researchers applied a current of electricity to niobium which generates a magnetic field that penetrates the layer of tantalum causing unpairing of superconducting material and causing cool down. The cold tantalum layer absorbs heat from the warmer copper layer. The magnetic field is slowly turned off causing tantalum to pair up again which causes tantalum to become hotter than niobium. The cycle repeats again which maintains a low temperature in the topmost copper layer.


magnetic levitation superconductivity

Scientists successfully demonstrate superconductivity at highest temperature till date

A group of researchers from the University of Chicago has observed superconductivity at the highest temperature recorded till date. With the help of highly developed technology at the Argonne National Laboratory, affiliated to UChicago, the team observed and studied a group of materials in which superconductivity was detected at a temperature of  -23 degrees Celsius (minus 9 degrees Fahrenheit, 250 K). This is an increase of almost 50 degrees from the previous record.

Although the superconductivity was observed at very high pressure, this observation is a huge step in achieving superconductivity at room temperatures. This is the ultimate goal of researchers using the technologies. The study has been published in the Nature journal. It has been authored by Vitali Prakapenka and Eran Greenberg, researchers at the University of Chicago.

Superconductivity was discovered in 1911 by a Dutch scientist Heike Kamerlingh Onnes. Materials which display superconductivity have two main characteristics, they do not offer any resistance to electricity and magnetic field lines cannot penetrate them. There are a wide range of applications of superconductivity such as high-speed supercomputers and train based on magnetic levitation.

Earlier researchers could only create superconducting materials at very low temperatures such as -240 degrees Celsius and -73 degrees Celsius very recently. It is quite expensive to achieve this level of cooling and thus it limits the application in the real world. Recently, theoretical studies have shown that a new group of materials, the superconducting hydrides can allow for superconductivity at higher temperatures.

Scientists at the Max Planck Institute in Germany and researchers at the University of Chicago collaborated to create such a material, the lanthanum superhydrides and then determined its composition. However for this to be achieved the material had to be placed under high pressures – within 150 and 170 gigapascals which is one and half million times larger than the sea level pressure. Under this large pressure, the material showed superconductivity.

In the experiment, three out of four characteristics to prove superconductivity were exhibited by the material. There was a drop in the electrical resistance and in the critical temperature under the influence of an external magnetic field. It also displayed a change in the temperature when some of the elements were replaced with isotopes. However, it did not show the Meissner effect as the size of the object is very small.

For the experiment, a very small sample of the object was inserted between two diamonds for the needed pressure to be exerted. After that, high energy X-rays from the Advanced Photon Source were used to determine the structure of the material. Scientists are looking for more efficient ways to achieve superconductivity at regular conditions.