Nav: Home

Spreading light over quantum computers

September 03, 2019

Scientists at Linköping University have shown how a quantum computer really works and have managed to simulate quantum computer properties in a classical computer. "Our results should be highly significant in determining how to build quantum computers", says Professor Jan-Åke Larsson.

The dream of superfast and powerful quantum computers has again been brought into focus, and large resources have been invested in research in Sweden, Europe and the world. A Swedish quantum computer is to be built within ten years, and the EU has designated quantum technology one of its flagship projects.

At the moment, few useful algorithms are available for quantum computers, but it is expected that the technology will be hugely significant in simulations of biological, chemical and physical systems that are far too complicated for even the most powerful computers currently available. A bit in a computer can take only the value one or zero, but a quantum bit can take all values in between. Simply put, this means that quantum computers do not need to take as many operations for each calculation they carry out.

Professor Jan-Åke Larsson and his doctoral student Niklas Johansson, in the Division for Information Coding at the Department of Electrical Engineering, Linköping University, have come to grips with what happens in a quantum computer and why it is more powerful than a classical computer. Their results have been published in the scientific journal Entropy.

"We have shown that the major difference is that quantum computers have two degrees of freedom for each bit. By simulating an additional degree of freedom in a classical computer, we can run some of the algorithms at the same speed as they would achieve in a quantum computer", says Jan-Åke Larsson.

They have constructed a simulation tool, Quantum Simulation Logic, QSL, that enables them to simulate the operation of a quantum computer in a classical computer. The simulation tool contains one, and only one, property that a quantum computer has that a classical computer does not: one extra degree of freedom for each bit that is part of the calculation.

"Thus, each bit has two degrees of freedom: it can be compared with a mechanical system in which each part has two degrees of freedom - position and speed. In this case, we deal with computation bits - which carry information about the result of the function, and phase bits - which carry information about the structure of the function", Jan-Åke Larsson explains.

They have used the simulation tool to study some of the quantum algorithms that manage the structure of the function. Several of the algorithms run as fast in the simulation as they would in a quantum computer.

"The result shows that the higher speed in quantum computers comes from their ability to store, process and retrieve information in one additional information-carrying degree of freedom. This enables us to better understand how quantum computers work. Also, this knowledge should make it easier to build quantum computers, since we know which property is most important for the quantum computer to work as expected", says Jan-Åke Larsson.

Jan-Åke Larsson and his co-workers have also supplemented their theoretical simulations with a physical version built with electronic components. The gates are similar to those used in quantum computers, and the toolkit simulates how a quantum computer works. With its help students, for example, can simulate and understand how quantum cryptography and quantum teleportation works, and also some of the most common quantum computing algorithms, such as Shor's algorithm for factorisation. (The algorithm works in the current version of the simulation but is equally fast - or slow - as in classical computers).
The LiU scientists founded a company in 2017. This has recently been included in a list drawn up by the of web journal EU-startups of the ten most interesting start-ups in Europe that "cool down the crazy world of quantum computing".

(The heading "10 European startups cooling down the crazy world of quantum computing" is a play on words, and refers to the fact that quantum computers normally require extensive cooling.)

Quantum Simulation Logic, Oracles, and the Quantum Advantage
Niklas Johansson and Jan-Åke Larsson
Department of Electrical Engineering, Linköping University, SE-581 83 Linköping, Sweden
Entropy 2019

Contact: Jan-Åke Larsson,, +46 13 28 14 68

Linköping University

Related Quantum Computers Articles:

Hot qubits break one of the biggest constraints to practical quantum computers
A proof-of-concept published today in Nature promises warmer, cheaper and more robust quantum computing.
Future quantum computers may pose threat to today's most-secure communications
Quantum computers that are exponentially faster than any of our current classical computers and are capable of code-breaking applications could be available in 12 to 15 years, posing major risks to the security of current communications systems, according to a new RAND Corporation report.
Novel error-correction scheme developed for quantum computers
Experimental quantum computers are plagued with errors. Here Dr Arne Grimsmo from the University of Sydney and colleagues from RMIT and the University of Queensland offer a novel method to reduce errors in a scheme applicable across different types of quantum hardware.
FEFU scientists developed method to build up functional elements of quantum computers
Scientists from Far Eastern Federal University (FEFU, Vladivostok, Russia), together with colleagues from FEB RAS, China, Hong Kong, and Australia, manufactured ultra-compact bright sources based on IR-emitting mercury telluride (HgTe) quantum dots (QDs), the future functional elements of quantum computers and advanced sensors.
ORNL researchers advance performance benchmark for quantum computers
Researchers at the Department of Energy's Oak Ridge National Laboratory (ORNL) have developed a quantum chemistry simulation benchmark to evaluate the performance of quantum devices and guide the development of applications for future quantum computers.
Quantum computers learn to mark their own work
A new test to check if a quantum computer is giving correct answers to questions beyond the scope of traditional computing could help the first quantum computer that can outperform a classical computer to be realised.
Blanket of light may give better quantum computers
Researchers from DTU Physics describe in an article in Science, how--by simple means -- they have created a 'carpet' of thousands of quantum-mechanically entangled light pulses.
One step closer future to quantum computers
Physicists at Uppsala University in Sweden have identified how to distinguish between true and 'fake' Majorana states in one of the most commonly used experimental setups, by means of supercurrent measurements.
Dartmouth research advances noise cancelling for quantum computers
The characterization of complex noise in quantum computers is a critical step toward making the systems more precise.
Spreading light over quantum computers
Scientists at Linköping University have shown how a quantum computer really works and have managed to simulate quantum computer properties in a classical computer.
More Quantum Computers News and Quantum Computers Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Making Amends
What makes a true apology? What does it mean to make amends for past mistakes? This hour, TED speakers explore how repairing the wrongs of the past is the first step toward healing for the future. Guests include historian and preservationist Brent Leggs, law professor Martha Minow, librarian Dawn Wacek, and playwright V (formerly Eve Ensler).
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.