Nav: Home

New method could enable more stable and scalable quantum computing, Penn physicists report

June 29, 2017

Researchers from the University of Pennsylvania, in collaboration with Johns Hopkins University and Goucher College, have discovered a new topological material which may enable fault-tolerant quantum computing. It is a form of computing that taps into the power of atoms and subatomic phenomena to perform calculations significantly faster than current computers and could potentially lead to advances in drug development and other complex systems.

The research, published in ACS Nano, was led by Jerome Mlack, a postdoctoral researcher in the Department of Physics & Astronomy in Penn's School of Arts & Sciences, and his mentors Nina Markovic, now an associate professor at Goucher, and Marija Drndic, Fay R. and Eugene L. Langberg Professor of Physics at Penn. Penn grad students Gopinath Danda and Sarah Friedensen, who received an NSF fellowship for this work, and Johns Hopkins Associate Research Professor Natalia Drichko and postdoc Atikur Rahman, now an assistant professor at the Indian Institute of Science Education and Research, Pune, also contributed to the study.

The research began while Mlack was a Ph.D. candidate at Johns Hopkins. He and other researchers were working on growing and making devices out of topological insulators, a type of material that doesn't conduct current through the bulk of the material but can carry current along its surface.

As the researchers were working with these materials, one of their devices blew up, similar to what would happen with a short circuit.

"It kind of melted a little bit," Mlack said, "and what we found is that, if we measured the resistance of this melted region of one of these devices, it became superconducting. Then, when we went back and looked at what happened to the material and tried to find out what elements were in there, we only saw bismuth selenide and palladium."

When superconducting materials are cooled, they can carry a current with zero electrical resistance without losing any energy.

Topological insulators with superconducting properties have been predicted to have great potential for creating a fault-tolerant quantum computer. However, it is difficult to make good electrical contact between the topological insulator and superconductor and to scale such devices for manufacture, using current techniques. If this new material could be recreated, it could potentially overcome both of these difficulties.

In standard computing, the smallest unit of data that makes up the computer and stores information, the binary digit, or bit, can have a value of either 0, for off, or 1, for on. Quantum computing takes advantage of a phenomenon called superposition, which means that the bits, in this case called qubits, can be 0 and 1 at the same time.

A famous way of illustrating this phenomenon is a thought experiment called Schrodinger's cat. In this thought experiment, there is a cat in a box, but one doesn't know if the cat is dead or alive until the box is opened. Before the box is opened, the cat can be considered both alive and dead, existing in two states at once, but, immediately upon opening the box, the cat's state, or in the case of qubits, the system's configuration, collapses into one: the cat is either alive or dead and the qubit is either 0 or 1.

"The idea is to encode information using these quantum states," Markovic said, "but in order to use it in needs to be encoded and exist long enough for you to read."

One of the major problems in the field of quantum computing is that the qubits are not very stable and it's very easy to destroy the quantum states. These topological materials provide a way of making these states live long enough for to read them off and do something with them, Markovic said.

"It's kind of like if the box in Schrodinger's cat were on the top of a flag pole and the slightest wind could just knock it off," Mlack said. "The idea is that these topological materials at least widen the diameter of the flag pole so the box is sitting on more a column than a flag pole. You can knock it off eventually, but it's otherwise very hard to break the box and find out what happened to the cat."

Although their initial discovery of this material was an accident, they were able to come up with a process to recreate it in a controlled way.

Markovic, who was Mlack's advisor at Johns Hopkins at the time, suggested that, in order to recreate it without having to continually blow up devices, they could thermally anneal it, a process in which they put it into a furnace and heat it to a certain temperature.

Using this method, the researchers wrote, "the metal directly enters the nanostructure, providing good electrical contact and can be easily patterned into the nanostructure using standard lithography, allowing for easy scalability of custom superconducting circuits in a topological insulator."

Although researchers already have the capability of making a superconducting topological material, there's a huge problem in the fact that, when they put two materials together, there's a crack in between, which decreases the electrical contact. This ruins the measurements that they can make as well as the physical phenomena that could lead to making devices that will allow for quantum computing.

By patterning it directly into the crystal, the superconductor is embedded, and there are none of these contact problems. The resistance is very low, and they can pattern devices for quantum computing in one single crystal.

To test the material's superconducting properties, they put it in two extremely cold refrigerators, one of which cools down to nearly absolute zero. They also swept a magnetic field across it, which would kill the superconductivity and the topological nature of the material, to find out the limitations of the material. They also did standard electrical measurements, running a current through and looking at the voltage that is created.

"I think what is also nice in this paper is the combination of the electrical transport performance and the direct insights from the actual device materials characterization," Drndic said. "We have good insights on the composition of these devices to support all these claims because we did elemental analysis to understand how these two materials join."

One of the benefits of the researchers' device is that it's potentially scalable, capable of fitting onto a chip similar to the ones currently in our computers.

"Right now the main advances in quantum computing involve very complicated lithography methods," Drndic said. "People are doing it with nanowires which are connected to these circuits. If you have single nanowires that are very, very tiny and then you have to put them in particular places, it's very difficult. Most of the people who are on the forefront of this research have multimillion-dollar facilities and lots of people behind them. But this, in principle, we can do in one lab. It allows for making these devices in a simple way. You can just go and write your device any way you want it to be."

According to Mlack, though there is still a fair amount of limitation on it; there's an entire field that has sprouted up devoted to coming up with new and interesting ways to try to leverage these quantum states and quantum information. If successful, quantum computing will allow for a number of things.

"It will allow for much faster decryption and encryption of information," he said, "which is why some of the big defense contractors in the NSA, as well as companies like Microsoft, are interested in it. It will also allow us to model quantum systems in a reasonable amount of time and is capable of doing certain calculations and simulations faster than one would typically be able to do."

It's particularly good for completely different kinds of problems, such as problems that require massive parallel computations, Markovic said. If you need to do lots of things at once, quantum computing speeds things up tremendously.

"There are problems right now that would take the age of the universe to compute," she said.

"With quantum computing, you'd be able to do it in minutes." This could potentially also lead to advances in drug development and other complex systems, as well as enable new technologies.

The researchers hope to start building some more advanced devices that are geared towards actually building a qubit out of the systems that they have, as well as trying out different metals to see if they can change the properties of the material.

"It really is a new potential way of fabricating these devices that no one has done before," Mlack said. "In general, when people make some of these materials by combining this topological material and superconductivity, it is a bulk crystal, so you don't really control where everything is. Here we can actually customize the pattern that we're making into the material itself. That's the most exciting part, especially when we start talking about adding in different types of metals that give it different characteristics, whether those be ferromagnetic materials or elements that might make it more insulating. We still have to see if it works, but there's a potential for creating these interesting customized circuits directly into the material."
-end-
This work was supported by the National Science Foundation through grants DGE-1232825, DMR-1507782 and EFRI 2-DARE 1542707.

University of Pennsylvania

Related Quantum Computing Articles:

A platform for stable quantum computing, a playground for exotic physics
Harvard University researchers have demonstrated the first material that can have both strongly correlated electron interactions and topological properties, which not only paves the way for more stable quantum computing but also an entirely new platform to explore the wild world of exotic physics.
Diversity may be key to reducing errors in quantum computing
In quantum computing, as in team building, a little diversity can help get the job done better, computer scientists have discovered.
'Valley states' in this 2D material could potentially be used for quantum computing
New research on 2-dimensional tungsten disulfide (WS2) could open the door to advances in quantum computing.
Sound of the future: A new analog to quantum computing
In a paper published in Nature Research's journal, Communications Physics, researchers in the University of Arizona Department of Materials Science and Engineering have demonstrated the possibility for acoustic waves in a classical environment to do the work of quantum information processing without the time limitations and fragility.
Imaging of exotic quantum particles as building blocks for quantum computing
Researchers have imaged an exotic quantum particle -- called a Majorana fermion -- that can be used as a building block for future qubits and eventually the realization of quantum computers.
Virginia Tech researchers lead breakthrough in quantum computing
A team of Virginia Tech chemistry and physics researchers have advanced quantum simulation by devising an algorithm that can more efficiently calculate the properties of molecules on a noisy quantum computer.
Limitation exposed in promising quantum computing material
Physicists have theorized that a new type of material, called a three-dimensional (3-D) topological insulator (TI), could be a candidate to create qubits for quantum computing due to its special properties.
New material shows high potential for quantum computing
A joint team of scientists at the University of California, Riverside, and the Massachusetts Institute of Technology is getting closer to confirming the existence of an exotic quantum particle called Majorana fermion, crucial for fault-tolerant quantum computing -- the kind of quantum computing that addresses errors during its operation.
A sound idea: a step towards quantum computing
Researchers at the University of Tsukuba and the University of Pittsburgh have developed a new method for using lasers to create tiny lattice waves inside silicon crystals that can encode quantum information.
Quantum computing boost from vapour stabilising technique
A technique to stabilise alkali metal vapour density using gold nanoparticles, so electrons can be accessed for applications including quantum computing, atom cooling and precision measurements, has been patented by scientists at the University of Bath.
More Quantum Computing News and Quantum Computing Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Accessing Better Health
Essential health care is a right, not a privilege ... or is it? This hour, TED speakers explore how we can give everyone access to a healthier way of life, despite who you are or where you live. Guests include physician Raj Panjabi, former NYC health commissioner Mary Bassett, researcher Michael Hendryx, and neuroscientist Rachel Wurzman.
Now Playing: Science for the People

#544 Prosperity Without Growth
The societies we live in are organised around growth, objects, and driving forward a constantly expanding economy as benchmarks of success and prosperity. But this growing consumption at all costs is at odds with our understanding of what our planet can support. How do we lower the environmental impact of economic activity? How do we redefine success and prosperity separate from GDP, which politicians and governments have focused on for decades? We speak with ecological economist Tim Jackson, Professor of Sustainable Development at the University of Surrey, Director of the Centre for the Understanding of Sustainable Propserity, and author of...
Now Playing: Radiolab

An Announcement from Radiolab