Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Physicists show that quantum ignorance is hard to expose

01.08.2011
The quantum world allows you to answer questions correctly when you don't even have all the information you should need

No-one likes a know-it-all but we expect to be able to catch them out: someone who acts like they know everything but doesn't can always be tripped up with a well-chosen question. Can't they? Not so. New research in quantum physics has shown that a quantum know-it-all could lack information about a subject as a whole, yet answer almost perfectly any question about the subject's parts. The work is published in Physical Review Letters.

"This is something conceptually very weird," says Stephanie Wehner of the Centre for Quantum Technologies at the National University of Singapore, who derived the theoretical result with PhD student Thomas Vidick at the University of California, Berkeley, United States. It's a new phenomenon to add to the list of philosophical conundrums in quantum physics – as strange as the quantum superposition or the quantum uncertainty principle. But the work also has practical motivation: understanding how information behaves in the quantum context is important in emerging technologies such as quantum cryptography and quantum computation.

To frame the problem, consider the example of someone answering questions about a book they have only half-read. If someone has incomplete knowledge about a book as a whole, one expects to be able to identify the source of their ignorance somewhere in the book's pages.

Wehner and Vidick simplify the situation to a book with two pages. They invite the usual quantum players, Alice and Bob, to collaborate. Alice reads the book and is allowed to give Bob one page's worth of information from it.

If Bob only has classical information, it is always possible to work out what he doesn't know. "We show that classically things are, well, sane" says Wehner. In other words, Bob's ignorance can be exposed. Imagine that Bob is a student trying to cheat in an exam, and the notes from Alice cover half the course. An examiner, having secretly inspected Bob's crib notes, could set questions that Bob couldn't answer.

The craziness comes if Bob gets one page's worth of quantum information from Alice. In this case, the researchers show, there is no-way to pinpoint what information Bob is missing. Challenge Bob, and he can guess either page of the book almost perfectly. An examiner could not expose Bob's ignorance even having seen his notes as long as the questions cover no more than half the course – the total amount of information Bob can recount cannot exceed the size of his notes.

It is an unexpected discovery. Researchers had been trying to prove that quantum ignorance would follow classical intuition and be traceable to ignorance of details, and finding that it isn't raises new questions. "We have observed this effect but we don't really understand where it comes from," says Wehner. An intuitive understanding may be forever out of reach, just as other effects in quantum theory defy mechanistic description. However, Wehner and Vidick have begun to design experimental tests and are already formulating a range of ways to explore this strange new frontier. In this work, they devised a means of encoding the quantum information from two pages into one that gave Bob, the quantum know-it-all, the ability to recount all but one bit of the information on either page (the last bit Bob would have to guess). They plan to test whether other encodings would be equally good.

Journal reference: T. Vidick and S. Wehner, "Does Ignorance of the Whole Imply Ignorance of the Parts? Large Violations of Noncontextuality in Quantum Theory", Physical Review Letters 107, 030402 (2011); http://prl.aps.org/abstract/PRL/v107/i3/e030402. A free preprint is available at http://arxiv.org/abs/1011.6448.

For more information, please contact:
Stephanie Wehner
Principal Investigator and Assistant Professor
Centre for Quantum Technologies
National University of Singapore
Email: wehner@comp.nus.edu.sg
Tel: +65 6601 1478
National University of Singapore
A leading global university centred in Asia, the National University of Singapore (NUS) is Singapore's flagship university which offers a global approach to education and research, with a focus on Asian perspectives and expertise.

NUS has 15 faculties and schools across three campus locations in Singapore – Kent Ridge, Bukit Timah and Outram. Its transformative education includes a broad-based curriculum underscored by multi-disciplinary courses and cross-faculty enrichment, as well as special programmes which allow students to realise their potential.

NUS has three Research Centres of Excellence (RCE) and 21 university-level research institutes and centres.

It is also a partner for Singapore's 5th RCE. The University shares a close affiliation with 16 national-level research institutes and centres. Research activities are strategic and robust, and NUS is well-known for its research strengths in engineering, life sciences and biomedicine, social sciences and natural sciences. It also strives to create a supportive and innovative environment to promote creative enterprise within its community. More at www.nus.edu.sg.

Centre for Quantum Technologies at the National University of Singapore

The Centre for Quantum Technologies (CQT) was established as Singapore's inaugural Research Centre of Excellence in December 2007. It brings together quantum physicists and computer scientists to explore the quantum nature of reality and quantum possibilities in information processing. CQT is funded by Singapore's National Research Foundation and Ministry of Education and is hosted by the National University of Singapore (NUS). More at www.quantumlah.org.

Jenny Hogan | EurekAlert!
Further information:
http://www.quantumlah.org

More articles from Physics and Astronomy:

nachricht Further Improvement of Qubit Lifetime for Quantum Computers
09.12.2016 | Forschungszentrum Jülich

nachricht Electron highway inside crystal
09.12.2016 | Julius-Maximilians-Universität Würzburg

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>