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2 for 1: NIST design enables more cost-effective quantum key distribution
May 30, 2008Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a simpler and potentially lower-cost method for distributing strings of digits, or "keys," for use in quantum cryptography, the most secure method of transmitting data. The new "quantum key distribution" (QKD) method, outlined in an upcoming paper,* minimizes the required number of detectors, by far the most costly components in quantum cryptography. Although this minimum-detector arrangement cuts transmission rates by half, the NIST system still works at broadband speeds, allowing, for example, real-time quantum encryption and decryption of webcam-quality video streams over an experimental quantum network.
In quantum cryptography, a recipient (named Bob) needs to measure a sequence of photons, or particles of light that are transmitted by a sender (named Alice). These photons have information encoded in their polarization, or direction of their electric field. In the most common polarization-based protocol, known as BB84, Bob uses four single-photon detectors, costing approximately $5,000-$20,000 each. One pair of detectors records photons with horizontal and vertical polarization, which could indicate 0 and 1 respectively. The other pair detects photons with "diagonal", or +/- 45 degree, polarization in which the "northeast" and "northwest" directions alternatively denote 0 and 1.
In the new method, the researchers, led by NIST's Xiao Tang, designed an optical component to make the diagonally polarized photons rotate by a further 45 degrees and arrive at the same detector but later, and into a separate "time bin", than the horizontal/vertical polarized ones. Therefore, one pair of detectors can be used to record information from both kinds of polarized photons in succession, reducing the required number of detectors from four to two. In another protocol, called B92, the researchers reduced the required number of detectors from two to one. And in work performed since their new paper, the researchers further developed their approach so that the popular BB84 method now only requires one detector instead of four.
Although in theory quantum cryptography can transmit absolutely secure keys guaranteed by fundamental physical principles (measuring them will disturb their values and make an eavesdropper instantly known), the imperfect properties of photon detectors may undermine system security in practice. For example, photon detectors have an intrinsic problem known as "dead time," in which a detector is out of commission for a short time after it records a photon, causing it to miss the bit of data that immediately follows; this could result in non-random (and therefore more predictable) bit patterns in which 0s alternate with 1s. Furthermore, inevitable performance differences between detector pairs can also cause them to record less random sequences of digits. The new design avoids these issues and maintains the security of quantum-key-distribution systems in practical applications.
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* L. Ma, T. Chang, A. Mink, O. Slattery, B. Hershman and X. Tang. Experimental demonstration of a detection-time-bin-shift polarization encoding quantum key distribution system. IEEE Communications Letters Vol. 12, No. 6, June 2008. In press.
National Institute of Standards and Technology (NIST)
Although in theory quantum cryptography can transmit absolutely secure keys guaranteed by fundamental physical principles (measuring them will disturb their values and make an eavesdropper instantly known), the imperfect properties of photon detectors may undermine system security in practice. For example, photon detectors have an intrinsic problem known as "dead time," in which a detector is out of commission for a short time after it records a photon, causing it to miss the bit of data that immediately follows; this could result in non-random (and therefore more predictable) bit patterns in which 0s alternate with 1s. Furthermore, inevitable performance differences between detector pairs can also cause them to record less random sequences of digits. The new design avoids these issues and maintains the security of quantum-key-distribution systems in practical applications.
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* L. Ma, T. Chang, A. Mink, O. Slattery, B. Hershman and X. Tang. Experimental demonstration of a detection-time-bin-shift polarization encoding quantum key distribution system. IEEE Communications Letters Vol. 12, No. 6, June 2008. In press.
National Institute of Standards and Technology (NIST)
Quantum Cryptography Current Events and Quantum Cryptography News RSSField experiment on a robust hierarchical metropolitan quantum cryptography network
Key Laboratory of Quantum Information (CAS), University of Science and Technology of China has recently demonstrated a metropolitan Quantum Cryptography Network (QCN) for Government Administration in Wuhu, China. Because of its scientific significance and social impact, the project is reported in Volume 54, Issue 17 (September, 2009) of the Chinese Science Bulletin authored by Fang-xing Xu et al.
UA scientists discover quantum fingerprints of chaos
Chaotic behavior is the rule, not the exception, in the world we experience through our senses, the world governed by the laws of classical physics.
Up-scale: Frequency converter enables ultra-high sensitivity infrared spectrometry
In what may prove to be a major development for scientists in fields ranging from forensics to quantum communications, researchers at the National Institute of Standards and Technology (NIST) have developed a new, highly sensitive, low-cost technique for measuring light in the near-infrared range.
Researchers unite to distribute quantum keys
Researchers from across Europe have united to build the largest quantum key distribution network ever built.
Scientists demonstrate all-fibre quantum logic
A team of physicists and engineers have demonstrated all-fibre quantum logic, where single photons are generated and used to perform the contolled-NOT quantum logic gate in optical fibres with high fidelity.
Computer hackers R.I.P. -- making quantum cryptography practical
Quantum cryptography, a completely secure means of communication, is much closer to being used practically as researchers from Toshiba and Cambridge University's Cavendish Laboratory have now developed high speed detectors capable of receiving information with much higher key rates, thereby able to receive more information faster.
Scientists demonstrate laser with controlled polarization
Applied scientists at the Harvard School of Engineering and Applied Sciences (SEAS) in collaboration with researchers from Hamamatsu Photonics in Hamamatsu City, Japan, have demonstrated, for the first time, lasers in which the direction of oscillation of the emitted radiation, known as polarization, can be designed and controlled at will.
U of T physicists are first to 'squeeze' light to quantum limit
A team of University of Toronto physicists have demonstrated a new technique to squeeze light to the fundamental quantum limit, a finding that has potential applications for high-precision measurement, next-generation atomic clocks, novel quantum computing and our most fundamental understanding of the universe.
Dream of quantum computing closer to reality as mathematicians chase key breakthrough
The ability to exploit the extraordinary properties of quantum mechanics in novel applications, such as a new generation of super-fast computers, has come closer following recent progress with some of the remaining underlying mathematical problems.
Light touch: Controlling the behavior of quantum dots
Researchers from the National Institute of Standards and Technology (NIST) and the Joint Quantum Institute (JQI), a collaborative center of the University of Maryland and NIST, have reported a new way to fine-tune the light coming from quantum dots by manipulating them with pairs of lasers.
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