The quantum revolution is a step closer: New way to run a quantum algorithm

 

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Dr Austin Lund (left) and Dr Anthony Laing, co-authors of the research.

Theories show how computing devices that operate according to quantum mechanics can solve problems that conventional (classical) computers, including super computers, can never solve. These theories have been experimentally tested for small-scale quantum systems, but the world is waiting for the first definitive demonstration of a quantum device that beats a classical computer.

Now, researchers from the Centre for Quantum Photonics (CQP) at the University of Bristol together with collaborators from the University of Queensland (UQ) and Imperial College London have increased the likelihood of such a demonstration in the near term by discovering a new way to run a quantum algorithm with much simpler methods than previously thought.

The first definitive defeat for a classical computer could be achieved with a quantum device that runs an algorithm known as Boson Sampling, recently developed by researchers at MIT.

Boson Sampling uses single photons of light and optical circuits to take samples from an exponentially large probability distribution, which has been proven to be extremely difficult for classical computers.

Unlike other quantum algorithms, Boson Sampling has the benefit of being practical for near-term implementations, with the only experimental drawback being the difficulty of generating the dozens of single photons required for the important quantum victory.

However, the Bristol-UQ-Imperial researchers have found that the Boson Sampling algorithm can still be proven to be hard for classical computers when using standard probabilistic methods to generate single photons.

Dr Anthony Laing who led the CQP elements of the research said: "We realised we could chain together many standard two-photon sources in such a way as to give a dramatic boost to the number of photons generated."

Dr Austin Lund from UQ and currently on sabbatical in CQP added: "Once we had the idea for the boosted source, we needed to prove that it could solve a version of the Boson Sampling algorithm. We hope that the last major experimental hurdle has now been overcome."

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Story Source:

The above story is based on materials provided by University of Bristol. Note: Materials may be edited for content and length.

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Journal Reference:

1. A. P. Lund, A. Laing, S. Rahimi-Keshari, T. Rudolph, J. L. O’Brien, T. C. Ralph. Boson Sampling from a Gaussian State. Physical Review Letters, 2014; 113 (10) DOI: 10.1103/PhysRevLett.113.100502

Proteins 'ring like bells': Quantum mechanics and biochemical reactions

 

June 3, 2014

University of Glasgow

As far back as 1948, Erwin Schrödinger -- the inventor of modern quantum mechanics -- published the book 'What is life?' In it, he suggested that quantum mechanics and coherent ringing might be at the basis of all biochemical reactions. At the time, this idea never found wide acceptance because it was generally assumed that vibrations in protein molecules would be too rapidly damped. Now, scientists have shown that he may have been on the right track after all.

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Dr David Turton, the ultrafast laser expert who carried out the laser experiments.

As far back as 1948, Erwin Schrödinger -- the inventor of modern quantum mechanics -- published the book "What is life?"

In it, he suggested that quantum mechanics and coherent ringing might be at the basis of all biochemical reactions. At the time, this idea never found wide acceptance because it was generally assumed that vibrations in protein molecules would be too rapidly damped.

Now, scientists at the University of Glasgow have demonstrated he was on the right track after all.

Using modern laser spectroscopy, the scientists have been able to measure the vibrational spectrum of the enzyme lysozyme, a protein that fights off bacteria. They discovered that this enzyme rings like a bell with a frequency of a few terahertz or a million-million hertz. Most remarkably, the ringing involves the entire protein, meaning the ringing motion could be responsible for the transfer of energy across proteins.

The experiments show that the ringing motion lasts for only a picosecond or one millionth of a millionth of a second. Biochemical reactions take place on a picosecond timescale and the scientists believe that evolution has optimised enzymes to ring for just the right amount of time. Any shorter, and biochemical reactions would become inefficient as energy is drained from the system too quickly. Any longer and the enzyme would simple oscillate forever: react, unreact, react, unreact, etc. The picosecond ringing time is just perfect for the most efficient reaction.

These tiny motions enable proteins to morph quickly so they can readily bind with other molecules, a process that is necessary for life to perform critical biological functions like absorbing oxygen and repairing cells.

The findings have been published in Nature Communications.

Klaas Wynne, Chair in Chemical Physics at the University of Glasgow said: "This research shows us that proteins have mechanical properties that are highly unexpected and geared towards maximising efficiency. Future work will show whether these mechanical properties can be used to understand the function of complex living systems."

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Story Source:

The above story is based on materials provided by University of Glasgow. Note: Materials may be edited for content and length.

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Journal Reference:

1. David A. Turton, Hans Martin Senn, Thomas Harwood, Adrian J. Lapthorn, Elizabeth M. Ellis, Klaas Wynne. Terahertz underdamped vibrational motion governs protein-ligand binding in solution. Nature Communications, 2014; 5 DOI: 10.1038/ncomms4999