World's fastest quantum random-number generator

Celia Elliott
5/17/2010

Ever since humans discovered gambling, people have sought improved means of generating random numbers—unpredictable outcomes based on a physical process such as coin flipping, dice throwing, or wheel spinning. But such methods are both too slow and too unreliable for modern applications requiring random numbers.

Now physicists at the University of Illinois at Urbana-Champaign have developed a novel method to generate random numbers at record speeds and security, using the laws of quantum mechanics. The new scheme, based on shaping the photon flux from a laser diode and then digitizing the time interval between random photon arrivals, is a factor of 10 faster than any other quantum random number generator reported so far, according to Bardeen Professor of Physics and of Electrical and Computer Engineering Paul G. Kwiat. The group’s results were published in Optics Express in April.

Random number generators are essential for a variety of applications, including data encryption, statistical analysis, and advanced numerical simulations. However, because of limitations in reading out truly random physical processes, many current applications employ a pseudo-random number generator—a deterministic method that replicates the behavior of a physical phenomenon that is expected to be random or a computational algorithm based on a shorter initial value, known as a “seed” or a “key.”

But some applications, such as quantum cryptography, require absolute randomness to ensure security. Explains Michael Wayne, who developed the new method as part of his graduate research in Electrical and Computing Engineering, “Most random number generators are not actually random, they are just so complex that the computational cost required to predict their outcome is too large for modern computers. As technology advances, this is no longer the case, and previously secure systems can be compromised.” Because quantum physics is intrinsically random, scientists have increasingly turned to quantum systems as a source of random data.

Quantum optics, the behavior of individual “particles” of light, called photons, has proven to be particularly amenable to generating and reading out the random binary numbers of great interest for secure information processing, encryption, and transmission. Most existing quantum random number generators rely on measuring the behavior of an incoming photon at a beam-splitter to create data. This approach has significant limitations, however, in that each photon can produce at most one bit of data, and the systems are heavily constrained by the rate at which single-photon detectors can operate.

The method developed by Kwiat’s group produces a fast quantum random number generator having reduced bias and requiring less post-processing. “Unlike existing methods, our method creates multiple random bits per detection event and greatly reduces the need for post-processing,” said Kwiat. “We are able to obtain fast, secure quantum random number generation at rates exceeding 100 Mbit/s. Even faster rates—exceeding 10 Gbit/s—may be possible with planned improvements to our laser driver circuit and detectors.”

Recent News

  • Research

An international team of researchers led by Paul Scherrer Institute postdoctoral researcher Niels Schröter now provide an important benchmark for how "strong" topological phenonena can be in a real material. Writing in Science, the team reports experiments in which they observed that, in the topological semimetal palladium gallium (PdGa), one of the most common classifiers of topological phenomena, the Chern number, can reach the maximum value that is allowed in any metallic crystal. That this is possible in a real material has never been shown before. Moreover, the team has established ways to control the sign of the Chern number, which might bring new opportunities for exploring, and exploiting, topological phenomena. Illinois Physics Professor Barry Bradlyn contributed to the theoretical work elucidating the team's experiments.

At the European Organization for Nuclear Research (CERN), over 200 physicists across dozens of institutions are collaborating on a project called COMPASS. This experiment (short for Common Muon and Proton Apparatus for Structure and Spectroscopy) uses CERN’s Super Proton Synchrotron to tear apart protons with a particle beam, allowing researchers to see the subatomic quarks and gluons that make up these building blocks of the universe. But particle beams aren’t the only futuretech in play – the experiments are also enabled by a heavy dose of supercomputing power.

New findings from physicists at the University of Illinois, in collaboration with researchers at The University of Tokyo and others, clarify the physics of coupling topological materials with simple, conventional superconductors.

Through a novel method they devised to fabricate bulk insulating topological insulator (TI) films on superconductor (SC) substrates, the researchers were able to more precisely test the proximity effect, or coupling when two materials contact one another, between TIs and SCs. They found that when the TI film is bulk insulating, no superconductivity is observed at the top surface, but if it is a metal, as in prior work, strong, long-range superconducting order is seen. The experimental efforts were led by physics Professor Tai-Chang Chiang and Joseph Andrew Hlevyack, postdoctoral researcher in Professor Chiang’s group, in collaboration with Professor James N. Eckstein’s group including Yang Bai, Professor Kozo Okazaki’s Lab at The U. of Tokyo, and five other institutes internationally. The findings are published in Physical Review Letters, which has been highlighted as a PRL Editors’ Suggestion.

  • Accolades

Illinois Physics Assistant Professor Barry Bradlyn has been selected for a 2020 National Science Foundation CAREER (Faculty Early Career Development) Award. This award is conferred annually in support of junior faculty who excel in the role of teacher-scholars by integrating outstanding research programs with excellent educational programs. Receipt of this award also reflects great promise for a lifetime of leadership within the recipients’ respective fields.

Bradlyn is a theoretical condensed matter physicist whose work studying the novel quantum properties inherent in topological insulators and topological semimetals has already shed new light on these extraordinary systems. Among his contributions, he developed a real-space formulation of topological band theory, allowing for the prediction of many new topological insulators and semimetals.