Blog: Bits of Reality

Bits of Reality
Science News (04/07/12) Vol. 181, No. 7, P. 26 Tom Siegfried

Information derived from quantum computing systems could reveal subtle insights about the intersection between mathematics and the physical world. "We hope to be able to verify that these extraordinary computational resources in quantum systems really are part of the way nature behaves," says California Institute of Technology physicist John Preskill. "We could do so by solving a problem that we think is hard classically ... with a quantum computer, where we can easily verify with a classical computer that the quantum computer got the right answer." To solve certain hard problems that standard supercomputers cannot accommodate, such as finding the prime factors of very large numbers, quantum computers must process bits of quantum information. Quantum machines would only be workable for problems that could be posed as an algorithm amenable to the way quantum weirdness can eliminate wrong answers, allowing only the right answer to prevail. In 2011, the Perimeter Institute for Theoretical Physics' Giulio Chiribella and colleagues demonstrated how to derive quantum mechanics from a set of five axioms plus one postulate, all rooted in information theory terms. The foundation of their system is axioms such as causality, the notion that signals from the future cannot impact the present.

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Blog: Multi-Purpose Photonic Chip Paves the Way to Programmable Quantum Processors

Multi-Purpose Photonic Chip Paves the Way to Programmable Quantum Processors
University of Bristol News (12/11/11)

University of Bristol researchers have developed an optical chip that generates, manipulates, and measures two quantum phenomena, entanglement and mixture, which are essential for building quantum computers. The researchers showed that entanglement can be generated, manipulated, and measured on a silicon chip. The chip also has been able to measure mixture, which can be used to characterize quantum circuits. "To build a quantum computer, we not only need to be able to control complex phenomena, such as entanglement and mixture, but we need to be able to do this on a chip, so that we can scalably and practically duplicate many such miniature circuits--in much the same way as the modern computers we have today," says Bristol professor Jeremy O'Brien. "Our device enables this and we believe it is a major step forward towards optical quantum computing." The chip consists of a network of tiny channels that guide, manipulate, and interact with single photons. "It’s exciting because we can perform many different experiments in a very straightforward way, using a single reconfigurable chip," says Bristol's Peter Shadbolt. The researchers are now scaling up the complexity of the device for use as a building block for quantum computers.

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Blog: Quantum Knowledge Cools Computers

Quantum Knowledge Cools Computers
ETH Zurich (06/01/11) Simone Ulmer

Researchers at ETH Zurich and the National University of Singapore have found that, under certain conditions, cold is generated instead of heat when deleting data if the memory is known "more than completely," as is the case during quantum-mechanical entanglement because it carries more information than a classical copy of the data. The Landauer's Principle states that energy is always released as heat when data is deleted. "According to Landauer's Principle, if a certain number of computing operations per second is exceeded, the heat generated can no longer be dissipated," which will put supercomputers at a critical limit in the next 10 to 20 years, says ETH Zurich professor Renato Renner. However, the new study shows that during quantum entanglement, the deletion operation becomes a reversible process and Landauer's Principle holds true. The researchers proved this mathematically by combining the entropy concepts from information theory and thermodynamics. "We have now shown that the notion of entropy actually describes the same thing in both cases," Renner says. The results show that in a quantum computer, the entropy would be negative, meaning that heat would be withdrawn from the environment and the machine would cool down.

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Blog: Software [using classical computing] Said to Match Quantum Computing Speed

Software Said to Match Quantum Computing Speed
IDG News Service (12/23/10) Joab Jackson

University of Waterloo researchers have shown that for some computing problems, using the right software algorithms could enable classical computing techniques to work just as well as quantum computing. The researchers demonstrated how a seldom-used algorithm could achieve new levels in problem-solving performance when used on contemporary computers and theoretically match quantum computing speeds. "One striking implication of this characterization is that it implies quantum computing provides no increase in computational power whatsoever over classical computing in the context of interactive proof systems," according to the paper. Massachusetts Institute of Technology professor Scott Aaronson and colleagues recently proved that quantum interactive proof systems are just as difficult to solve as classical interactive proof systems, by using the matrix multiplicative weights update method to devise a new algorithm. The algorithm provides a method for solving problems using parallel processes, matching the efficiency of quantum computing. The researchers illustrated that "for a certain class of semi-definite programs you can get not the exact answer but a very good approximate answer, using a very small amount of memory," Aaronson says.

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Blog: Quantum Links Let Computers Understand Language

Quantum Links Let Computers Understand Language
New Scientist (12/08/10) Jason Aron

University of Oxford researchers are using a form of graphical mathematics to develop an approach to linguistics that could enable computers to make sense of language. Oxford's Bob Coecke and Samson Abramsky used a graphical form of the category theory, a branch of mathematics that allows different objects within a collection to be linked, to formulate quantum mechanical problems more intuitively by providing a way to link quantum objects. The researchers are using that graphical approach to create a universal theory of meaning in which language and grammar are encoded as mathematical rules. Most existing human language models focus on deciphering the meaning of individual words, or the rules of grammar, but not both. The researchers combined the existing models using the graphical approach that was designed for quantum mechanics. Coecke developed an algorithm that connects individual words. The Oxford team plans to teach the system using a billion pieces of text taken from legal and medical documents.

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Blog: Optical Chip Enables New Approach to Quantum Computing

Optical Chip Enables New Approach to Quantum Computing
University of Bristol News (09/16/10) Aliya Mughal

An international research team led by University of Bristol scientists has developed a silicon chip for quantum computing that could be used to perform complex calculations. "We believe, using our new technique, a quantum computer could, in less than 10 years, be performing calculations that are outside the capabilities of conventional computers," says Bristol professor Jeremy O'Brien. The technique uses two identical particles of light moving along a network of circuits in the silicon chip to perform an experiment called a quantum walk. "Using a two-photon system, we can perform calculations that are exponentially more complex than before," O'Brien says. The researchers say that a quantum computer based on a multi-photon quantum walk could be used to simulate complex processes such as superconductivity and photosynthesis. "Our technique could improve our understanding of such important processes and help, for example, in the development of more efficient solar cells," O'Brien says. Other applications could include the development of ultra-fast and efficient search engines, designing high-tech materials, and new pharmaceuticals.

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Blog: Quantum Crypto Products Cracked By Researchers

Quantum Crypto Products Cracked By Researchers
Government Computer News (09/10/10) William Jackson

A European research team has shown that commercial implementations of quantum key distribution (QKD) are subject to eavesdropping with off-the-shelf materials. "Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumination," the researchers write. However, U.S. National Institute of Standards and Technology scientist Xiao Tang disputes their conclusion, saying the attack technique can be prevented. "This type of attack is not new and is based on the idea of the intercept-resend attack," in which the eavesdropper intercepts information and then passes it along to the intended recipient, he says. Although the European researchers demonstrated a practical implementation of the attack, Tang says it can be easily prevented. The European demonstration is not meant to discredit QKD, but to strengthen an emerging technology. "Rather than demonstrating that practical QKD cannot become provably secure, our findings clearly show the necessity of investigating the practical security of QKD," write the researchers.

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Blog: Quantum Cryptography Breached With Lasers

Quantum Cryptography Breached With Lasers
InformationWeek (09/08/10) Mathew J. Schwartz

The Norwegian University of Science and Technology (NTNU), the University of Erlangen-Nurnberg, and the Max Planck Institute collaborated to develop a laser-based attack against quantum cryptography systems that allows them to eavesdrop on communications without revealing their presence. The researchers developed a quantum eavesdropping technique that remotely controls the photon detector, which is a key component in most quantum cryptography systems. The researchers believe that cyberattackers could breach security systems with off-the-shelf components, and obtain a perfect copy of the raw key without leaving any trace of their presence. "The security loophole we have exposed is intrinsic to a whole class of single-photon detectors, regardless of their manufacturer and model," says NTNU researcher Vadim Makarov.

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Blog: More Accurate Than Heisenberg Allows?

More Accurate Than Heisenberg Allows?
Ludwig-Maximilians-Universitat Munchen (07/27/10)

Quantum cryptography is the safest data encryption method, and takes advantage of the fact that transmitted information can only be quantified with a strictly limited degree of precision. Scientists at ETH Zurich and Ludwig-Maximilians-Universitat (LMU) in Munich have made a discovery in how the use of a quantum memory impacts this uncertainty. "The result not only enhances our understanding of quantum memories, it also provides us with a method for determining the degree of correlation between two quantum particles," says ETH Zurich professor Matthias Christandl. "Moreover, the effect we have observed could yield a means of testing the security of quantum cryptographic systems." Quantum mechanics dictates that the measurement of a parameter can itself disturb a particle's state, and this effect is harnessed by quantum cryptography to encrypt data and thwart eavesdropping. The LMU and ETH Zurich teams have demonstrated that the result of a measurement on a quantum particle can be predicted with greater accuracy if data about the particle is contained in a quantum memory, which can consist of atoms or ions.

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Blog: Toshiba Invention Brings Quantum Computing Closer

Toshiba Invention Brings Quantum Computing Closer
Reuters (06/02/10) Hirschler, Ben

Researchers at Toshiba's research center in Cambridge, England, have designed a device that could open the way to super-fast quantum computing through the development of ultra-powerful semiconductors. Toshiba's Entangled Light Emitting Diode (ELED) is an easy-to-assemble device that can be connected to a battery to generate entangled light on an as-needed basis. Quantum computers based on optical processes require a large number of entangled photons, and producing entangled light has up to now been limited to bulky lasers. The ELED device employs standard semiconductor technology and is fashioned from gallium arsenide, a common material in optoelectronics. Although similar to conventional light-emitting diodes, the ELED contains a quantum dot that transforms electrical current into entangled light. "It's a big step because it means you can now start to integrate lots of devices on a single chip," says lead researcher Andrew Shields. He believes that basic quantum computing circuits that use ELED technology could be ready within five years.

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Blog: Random, But Not By Accident: Quantum Mechanics and Data Encryption

Random, But Not By Accident: Quantum Mechanics and Data Encryption
UM Newsdesk (04/13/10) Tune, Lee

Researchers at the University of Maryland's Joint Quantum Institute (JQI), working with European quantum information scientists, have demonstrated a method of producing certifiably random strings of numbers based on the fundamental principles of quantum mechanics. The technique is based on the work of physicist John Bell, who studied a condition called entanglement, in which matter particles become so interdependent that if a measurement is performed to determine a property of one, which will be a random value, the corresponding property of the other is instantly determined as well. Bell showed mathematically that if the objects were not entangled, their correlations would have to be smaller than a certain value, expressed as an "inequality." However, if they were entangled, their correlations could be higher, violating the inequality. The JQI test was the first to violate a Bell inequality between systems separated over a distance without missing any of the events. "If we verify a Bell inequality violation between isolated systems while not missing events, we can ensure that our device produces private randomness," says JQI's Dzmitry Matsukevich.

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Blog: Aussie Quantum Experiment Challenges Einstein, Computer Science

Aussie Quantum Experiment Challenges Einstein, Computer Science
Computerworld Australia (01/12/10) Pauli, Darren

University of Queensland (UQ) and Harvard University researchers have completed an experiment that could have massive ramifications for science through the application of quantum mechanics to chemistry to predict molecular reactions. Project co-author and UQ professor Andrew White says the existence of quantum computing implies that either quantum mechanics is incorrect or computer science's underlying Church Turing Thesis is faulty. "What we have done is a 2 qubit [quantum bit], toy experiment--it won't put anyone out of a job anytime soon ... but if we scale to tens and then hundreds of qubits, that's when we will exceed the computational capacity of the planet ... that will happen [within] 50 years," White says. The experiment ran an algorithm called the iterative phase estimation to quantify the exact energy of molecular hydrogen against a predicted model. White calls the results, which were accurate inside of six parts in 1 million, "astounding." Data was calculated to 20 bits, and in some cases as many as 47 bits, and experiments were redone 30 times for classical error correction. White theorizes that the experiment's results could be utilized to forecast the outcome of chemical reactions without the innate randomness missing from controlled computer simulations.

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Blog: Quantum Computers Will Require Complex Software to Manage Errors

Quantum Computers Will Require Complex Software to Manage Errors
National Institute of Standards and Technology (04/07/09) Boutin, Chad

National Institute of Standards and Technology (NIST) theorists have demonstrated that a type of software operation, believed to be a solution to the fundamental problems with computer hardware, will not function as originally hoped, adding additional complexity to the development of quantum computers. If quantum computers are ever realized, they will use effects associated with atomic physics to solve enormously complicated problems. Prototype quantum processors have proven to be prone to errors caused by noise from stray electric or magnetic fields. To make error correction more efficient, researchers are designing quantum computing architectures to limit errors, including creating software that does not permit qubits to interact if their errors could compound one another. Quantum software with this property is called "transversal encoded quantum gates." However, the NIST team has proven that this software, which is heavily studied due to its simplicity and robustness against interfering noise, is insufficient for performing arbitrary computations, meaning any software that quantum computers use will have to be far more complicated and resource-intensive to ensure devices work properly. The NIST researchers mathematically proved that transversal gates cannot be used exclusively and that more complex solutions for error management and correction need to be found and deployed.

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Blog: A New Step Towards Quantum Computers

A New Step Towards Quantum Computers
Ruhr-University Bochum (Germany) (03/28/09)

Researchers from Dortmound, St. Petersburg, Washington, and the Rurh-Universitaet-Bochum (RUB) in Germany have succeeded in aligning electron spin. The researchers also were able to rotate the spin, using a laser pulse, in any desired direction at any time, as well as read the direction with another laser pulse. "This is the first, important step toward addressing these 'quantum bits,' which will form an integral part of data transfer systems and processors in the future," says RUB professor Andreas Wieck. By applying an external magnetic field, an electron's spin can be accelerated or decelerated, causing it to waver and rotate its axis to virtually any desired angle. If these variations could be used to carry information it would be possible to store more than just 0s and 1s in an electron. A single electron has a very small measurable effect, requiring highly sensitive instruments, but by grouping electrons into ensembles the researchers created signals that are stronger by a magnitude of six, making them very sturdy and enabling the signals to be easily recorded. The team managed to confine nearly one million electrons each in virtually identical indium-arsenic islands, or quantum dots, improving their measurable effect.

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Blog: Fighting Tomorrow's Hackers

Fighting Tomorrow's Hackers
American Friends of Tel Aviv University (02/05/09)

The development of quantum computing threatens to expose the security of digital information as the technology could be used to bypass the current cryptographic systems used by businesses and banks. "We need to develop a new encryption system now, before our current systems... become instantly obsolete with the advent of the first quantum computer," says Oded Regev, a professor at Tel Aviv University's Blavantnik School of Computer Science. Regev has proposed a secure and efficient system that is backed by a mathematical proof of security and believed to be the first solution safe from quantum computers. Regev combined ideas from quantum computation with research from other leaders in the field to create a system that is efficient enough for real-world applications. Regev first presented his work at the ACM Symposium on Theory of Computing, and it will appear in the Journal of the ACM. The work also will become the foundation for other cryptographic systems projects at the Stanford Research Institute, Stanford University, and the Massachusetts Institute of Technology. Regev's proposed system could have a variety of real-world applications, including banking transactions, online auctions, and digital signatures.

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Research: Beating the Codebreakers With Quantum Cryptography

Beating the Codebreakers With Quantum Cryptography
ICT Results (04/28/08)

Cryptography has been an arms race, with codemakers and hackers constantly updating their arsenals, but quantum cryptography could theoretically give codemakers the upper hand. Even the absolute best in classical encryption, the 128-bit RSA, can be cracked using brute force computing power. However, quantum cryptography could make possible uncrackable code using quantum key distribution (QKD). Modern cryptography relies on the use of digital keys to encrypt data before sending it over a network so it can be decrypted by the recipient. QKD promises a theoretically uncrackable code, one that can be easily distributed and still be transparent. Additionally, the nature of quantum mechanics makes it so that if an eavesdropper tries to intercept or spy on the transmission, both the sender and the receiver will know. Any attempt to read the transmission will alert the sender and the receiver, allowing them to generate a new key to send securely. QKD had its first real-world application in Geneva, where quantum cryptography was used in the electronic voting system. Not only did QKD guarantee that the poll was secure, but it also ensured that no votes were lost in transmission, because the uncertainty principle established that there were no changes in the transmitted data. The SECOQC project, which did the work for the voting system, says the goal is to establish network-wide quantum encryption that can work over longer distances between multiple parties.
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Research: McCormick Researchers Take Step Toward Creating Quantum Computers

McCormick Researchers Take Step Toward Creating Quantum Computers
Northwestern University (04/04/08)

Northwestern University researchers have demonstrated one of the basic building blocks for distributed quantum computing using entangled photons generated in optical fibers. "Because it is done with fiber and the technology that is already globally deployed, we think that it is a significant step in harnessing the power of quantum computers," says Northwestern professor Prem Kumar. The superposition of a quantum bit, or qubit, would allow a quantum computer to process significantly more information than a traditional computer. Kumar's group, which uses photons as qubits, found that they can entangle two indistinguishable photons in an optical fiber by using the fiber's inherent nonlinear response. The researchers also found that no matter how far the two photons are separated in standard transmission fibers, they remain entangled and "mysteriously" connected to each other's quantum state. Kumar and his team used the fiber-generated indistinguishable photons to implement the most basic quantum computer task, a controlled-NOT gate, which allows two photonic qubits to interact. DARPA has funded the group's next research effort, which will study how to implement a quantum network for physically demonstrating efficient public goods strategies, such as government contract auctions that would be able to find the most inexpensive contract arrangements by pairing contractors that have previous experience working together.
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Security: 'Half-Quantum' Cryptography Promises Total Security; quantum-encrypted key only

'Half-Quantum' Cryptography Promises Total Security
New Scientist (10/21/07) Marks, Paul

Many cryptographers believed that the only way to achieve complete security when transmitting information was to use quantum cryptography to share the key used for encryption. However, researchers say they can achieve the same level of security even if one party stays in the world of classical physics. In conventional quantum cryptography, a sender, dubbed Alice, generates a string of 0s and 1s and encodes them using a photon polarized in either the computational "basis" in which 0 and 1 are represented by vertical and horizontal polarizations, or in diagonal bases in which 1 and 0 are represented by 45 degree and negative 45 degree polarizations. When the photons arrive at their destination, the receiver, dubbed Bob, chooses either the computational or diagonal bases to measure each one, telling Alice which he has chosen. If the chosen basis is wrong, Alice tells Bob to discard that bit. The bits that are guessed correctly form the secret key. If an eavesdropper intercepts any photons, the stream is interrupted and Bob's ability to read a number of the photons he might have read correctly is destroyed. The increase in unreadable photons tells Bob the communication channel has been compromised. Researchers at the Israel Institute of Technology in Haifa and the University of Montreal have demonstrated that only Alice needs to be quantum-equipped. Alice encodes the bits as usual, though Bob can only use the computational basis. Bob randomly measures some of the received photons and returns the rest to Alice untouched. The bits read in the computational basis form the key. The system is still secure because anyone eavesdropping does not know which photons will be returned to Alice unmeasured.
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