Two for One: New Design Enables More Cost-Effective Quantum Key Distribution

May 29, 2008
Two for One: NIST Design Enables More Cost-Effective Quantum Key Distribution
A highly simplified schematic of a recipient's detectors in a quantum cryptography setup. Conventional cryptography setups (left) require at least two detectors, and the most common setup, known as BB84, requires four. By adding an optical component that delays the travel of photons to the detector, the number of required detectors is cut in half. Credit: NIST

Researchers at the National Institute of Standards and Technology 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.

Citation: 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.

Source: National Institute of Standards and Technology

Explore further: Tiny magnetic sensor deemed attractive

add to favorites email to friend print save as pdf

Related Stories

New high-resolution X-ray spectrometer for beam lines

Oct 28, 2014

NIST scientists have pioneered a technology that may speed the arrival of long-awaited materials and devices including advanced high-temperature superconductors and high-efficiency photovoltaic cells: A new ...

Superconducting circuits, simplified

Oct 17, 2014

Computer chips with superconducting circuits—circuits with zero electrical resistance—would be 50 to 100 times as energy-efficient as today's chips, an attractive trait given the increasing power consumption ...

Recommended for you

Tiny magnetic sensor deemed attractive

7 hours ago

Ultra-sensitive magnetic sensor technology pioneered at PML may soon be commercialized for a host of applications from detection of unexploded bombs and underground pipes to geophysical surveying and perhaps ...

Beams come knocking on the LHC's door

7 hours ago

Over the weekend, proton beams came knocking on the Large Hadron Collider's (LHC) door. Shooting from the Super Proton Synchrotron (SPS) and into the two LHC injection lines, the proton beams were stopped ...

Climate control in termite mounds

9 hours ago

When they make their way into homes, some species of termites can be destructive pests. Their fungus-harvesting relatives in Africa and Asia, however, are known for their construction prowess, collectively ...

The secret of dragonflies' flight

10 hours ago

Dragonflies can easily right themselves and maneuver tight turns while flying. Each of their four wings is controlled by separate muscles, giving them exquisite control over their flight.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.