Thursday, Oct. 8, 1998
Photo at left, William Buttler (P-23) prepares to generate and transmit a stream of individual photons used to form a "quantum key" for encrypting messages in experiments currently underway at TA-53. The Los Alamos research team, of which Buttler is a member, have years of success establishing quantum keys through optical fibers and now are engaged in transmitting the single photon-based messages through free space. Quantum keys are used to create secret messages that are immune to tampering and can only be translated with the unique key formed in communications between sender and receiver. At right, Glen Peterson (P-23) readies equipment for receiving the transmission used in creating a quantum key for encrypting messages. The telescope captures the individual photons as they arrive and directs them along one of two optical paths for analysis. The sender and receiver compare the characteristics of the photons they transmit and receive to generate the quantum key, which is known only to them. Photos by Edwin Vigil
Encryption advance for secure global communications
Scientists at the Laboratory have achieved a significant advance in demonstrating the viability of an unbreakable encryption scheme for transmitting secure communications to and from satellites.
The encryption scheme, based on randomly generated characteristics of individual photons, could make major financial transactions or key military communications impenetrable to attempts to crack them and capable of revealing any attempts to eavesdrop on them.
"This remarkable advance in unbreakable cryptographic systems illustrates how our national laboratories can take fundamental scientific concepts -- sometimes involving physics too deep for most of us to understand -- and turn them into practical applications that support our national security objectives and other societal needs," Energy Secretary Bill Richardson said.
Laboratory researchers have years of success transmitting their photon-based "quantum cryptographic keys" for encoding messages over optical fibers, a method useful for secure communications between fiber-linked facilities. Their latest achievement, described in the Oct. 12 issue of Physical Review Letters, was to successfully transmit a quantum key through the air over a distance of about one kilometer, demonstrating the feasibility of using the technique for secure satellite communications.
"This is an important result for our quantum key distribution system," said lead author William Buttler of Neutron Science and Technology (P-23), "because it's the lowest few kilometers of the atmosphere that will cause an optical beam to deviate the most. We've shown we can operate this system in the lowest portion of the atmospheric boundary layer, where turbulence is at its worst."
If the optical signal emerges mostly intact after passing through the boundary layer, the rest of the travel to a satellite orbiting 300 kilometers or so overhead will have negligible effect on the signal.
The PRL paper describes nighttime transmission and detection of the individual photons used to build the quantum cryptographic key for encoding and decoding messages. The researchers are now conducting their demonstration in daylight, an immensely more difficult challenge. The initial results of the daytime demonstration have been positive.
Encryption works by converting a message into a new form with a secret key. The key could be as simple as making A=1, B=2, C=3, etc. and writing the message in numbers. If the sender and recipient share the key, then decoding the message is straightforward.
Existing encryption schemes used to protect financial transactions, national security information and other significant communications suffer two weaknesses: the numerical-based keys used to encrypt messages are potentially vulnerable as computers become more powerful, and the key can possibly be intercepted when recipient and sender share it.
Quantum cryptographic keys, by contrast, are generated as needed between the sender and receiver, creating a random string of numbers known only to the two people. The key is created through their shared communication, and any attempts to intercept the communication or eavesdrop on it can be detected because of the quantum-based nature of the information.
Once the sender and receiver share a unique key, they can code, transmit and decode messages securely.
The Laboratory demonstration consists of a laser that can emit extremely short pulses; an attenuator that damps each pulse to a single photon, on average; and a system that randomly assigns one of two polarization states to the photon. The two polarization states represent "1" and "0" in a binary number sequence
Polarization describes a preferred direction of oscillation for the electromagnetic wave of a photon. Devices known as polarizers will transmit only specific polarization states.
The receiver includes a telescope and optics that randomly direct the photons collected along one of two paths, each configured to look for a specific polarization state.
The quantum key is generated when the sender, conventionally dubbed "Alice," generates a series of individual photons, shot out at a rate of a million per second, and randomly changes the polarization to create a sequence of zeroes and ones. She has told the recipient, dubbed "Bob," which polarization state represents a one and which a zero; this information can also be shared with the world at large without threatening the encryption scheme.
Bob captures as many of the incoming photons as possible, given the difficulty of plucking specific individual photons out of a sea of background photons. The Lab team has shown that with precision timing and properly chosen filters a sufficiently high number of photons can be detected to make the quantum encryption scheme work.
Bob's receiver randomly switches between his chosen polarization values for zero and one. He doesn't, however, try to measure Alice's original polarization states; instead, he looks for related polarization states. This ensures that when Bob is looking for a zero, he will never see a photon if Alice transmitted a one. Yet, a fraction of the time that he is looking for a zero and Alice transmits a zero, he will record a photon and know their two values were in agreement.
In less than a second, Alice can transmit a sequence of many thousands of photons. Bob will detect and agree with the value of some random fraction of these, about a quarter of the original photon stream on average. Bob then indicates the positions in the sequence where his value agreed with Alice's. This positional information, in which only Bob and Alice know the values for each point in agreement, allows them to form their secret quantum key.
If anyone intercepts the stream of photons the act will reveal itself by raising the error rate above a threshold value or eliminating the photon stream altogether.
The Laboratory's quantum key transmission operates at a wavelength that passes through the atmosphere with high efficiency and where high-quality detectors are commercially available. Generating the single-photon quantum key is a routine procedure for the system the Lab team has developed.
Authors on the PRL paper were Buttler, Richard Hughes, Paul Kwiat, Steve Lamoreaux, George Morgan, Glen Peterson and Chuck Simmons of Neutron Science and Technology (P-23); Gabe Luther of Hydrodynamic and X-ray Physics (P-22); and Beth Nordholt of Space and Atmospheric Sciences (NIS-1).
--John R. Gustafson
Postdoctoral prize winner to present colloquium today
1998 Postdoctoral Prize winner Brian Kendrick of Theoretical Chemistry
and Molecular Physics (T-12), will present a summary of his winning paper
at 3:45 p.m. today in the Physics Building Auditorium. The title of his
winning paper is "The Geometric (Berry) Phase and Its Effects in Molecular
Spectra and Scattering."
Kendrick will receive $500 and a certificate during the colloquium. The prize money is provided by Laboratory Associate Leon Heller, who created the prize back in 1976 and has paid the cash award out of his own pocket since the program's inception. The award is given to a Lab postdoctoral appointee for the best article in theoretical physics (any theoretical analysis of physical systems) that is published or accepted for publication by a certain date.
Kendrick, now a T-12 technical staff member, has been at the Lab about five years. He graduated Summa Cum Laude with a bachelor's degree in electrical engineering from Texas Tech University in 1987 and received his doctorate in physics from the University of Texas at Austin in 1992.
Refreshments for the colloquium will be served beginning at 3:15 p.m.
The following information was in a news release issued by the Santa Fe Institute Oct. 2.
Aggressive treatment for hepatitis C may be needed
Early findings indicate aggressive treatment for hepatitis C may be needed to arrest disease development
Researchers from the Laboratory, the University of Illinois, the University of Washington, Bar-Ilan University in Israel and the Santa Fe Institute have demonstrated in short-term clinical trails that the drug interferon-a-2b, given in doses of 10 to 15 million international units per day, can block up to 95 percent of hepatitis C virus production. The current treatment level approved by the Federal Drug Administration is 3 mIUs three times per week, which is less effective.
Hepatitis C is a chronic illness that over time can result in cirrhosis or liver cancer. It is a difficult virus to study in a laboratory setting as it cannot be grown in a cell culture, and animal studies to date have not been effective. "With the recent success of patient response to HIV therapy that included mathematical modeling of the kinetics of virus replication, experimentalists and theorists once again came together to see if a similar approach to studying and treating hepatitis C might provide similar beneficial results," said Avidan Neumann of the department of life sciences at Bar-Ilan University and an external faculty member at the Santa Fe Institute.
The analysis shows that heptitis C virus is more rapidly produced than HIV with approximately a trillion virus particles produced and cleared each day.
The study consisted of 23 untreated patients infected with hepatitis C randomly assigned to take one of three dose regimens from 5, 10 or 15 mIUs daily for 14 days, followed by treatment with 5 mIU daily. Blood samples were collected every few hours the first two days and then daily for two weeks. For those patients taking either 10 or 15 mIUs, the first two days showed dramatic clearing of the virus followed by a slower stabilized decline for the remaining test period. The rate of this slower stabilized decline appears predictive of whether the virus level in the blood becomes sufficiently low that it is undetectable by current technology after three months.
"These results show that hepatitis C infection, like HIV infection, is highly dynamic with large amounts of virus being rapidly produced in infected individuals. Modifying the current treatment of hepatitis C with increased dosages of itnerferon given daily helps the body rapidly clear the virus from the blood. While the long-term effects on disease progression are unknown, these findings suggest that more effective treatment for individuals inflicted with this disease may be possible," said Alan Perelson, leader of Theoretical Biology and Biophysics (T-10) and director of the Joseph P. and Jeanne M. Sullivan Theoretical Immunology Program at the Santa Fe Institute.
The report, published last week in the scientific journal Science, was released after following the subjects for three months. More longitudinal studies, as well as studies with more subjects are needed to verify results. However, initial results support the hypothesis that interferon works in combating the disease by blocking infected cells from either producing or releasing the virus; the data and analysis show that the degree of blockage is dependent on the dose; and that doses higher than the 3 mIUs currently given may be needed to combat the disease effectively.
The October issue of "Reflections" is now available -- the mailroom began distributing copies this week. Featured in this month's issue are the Laboratory's latest group of Distinguished Performers and more. |
New display panels in Administration Building
Employees and visitors to the Laboratory's Administration Building will see new posters in the display panels beginning Friday.
The informational posters near the east elevator around the corner from the Administration Building Auditorium are a project of the Science and Technology Base (STB) Program Office and LA Science.
The 42-panel display cases feature posters highlighting the Laboratory's outstanding research thrusts and achievements in science and technology, said Nikki Cooper of LA Science and coordinator of the project.
Laboratory Director John Browne and STB Director Al Sattelberger will host a reception at 12:45 p.m. Friday to unveil the new posters.
The new display posters feature the Computing, Information and Communications (CIC), Life Sciences (LS), and Earth and Environmental Sciences (EES) divisions, Nuclear Weapons (NW) Directorate, Accelerator Production of Tritium (APT) and the Los Alamos Neutron Science Center (LANSCE).
There are four additional posters, titled "Hidden Resources," which feature Lab employees Sam Bame of Space and Atmospheric Sciences (NIS-1), Donna Gadbois of Cell Molecular Biology (LS-4), Ellie Habbersett of Detonation Theory and Application (T-14), Ed Heighway of Laboratory Directed Research and Development (STB-LDRD), Santiago Jaramillo of Materials Management (BUS-4), Robert Owczarek and Hanna Makaruk, both of Complex Systems (T-13) and Sue Rabener of the Human Resources (HR) Division Office.
Four posters titled "New Directions," feature Mike Warren of Theoretical Astrophysics' (T-6) and his work in commodity supercomputing.
The informational posters are mounted on foam core board. The panels measure 18 inches wide by 48 inch long. At the bottom of each poster is the name of the Lab staff member and his or her telephone number to contact for more information.
The posters currently in the display cases in the Administration Building feature Physics (P), Applied Theoretical and Computational Physics (X), Theoretical (T), Technology and Safety Assessment (TSA) divisions as well as the Lab's diversity working groups. They will be moved to the Otowi Building for three weeks and then to the J. Robert Oppenheimer Study Center, said Cooper.
"This is a community project," said Cooper. "We hope it will help build morale and a sense of community spirit. The idea is to highlight research at the Lab, as well as human resources and institutional initiatives. We expect people to offer suggestions [on new posters]."
Cooper said a Lab committee coordinated by STB has proposed a schedule of rotation, with Lab technical divisions and technical program offices mounting one display every two years. Each technical division/program office will have six posters (three cases) for its display; each display hangs for six months.
Posters are reviewed before they are mounted for classification, text editing and safety considerations, said Cooper.
She credited other LA Science team members and Communication Arts and Services (CIC-1) employees who were involved in the design and production of the posters.
Cooper said Lab organizations interested in participating in the project must pay the cost of producing and mounting the posters in the Administration Building.
Employees who have suggestions for future posters can call Cooper at 7-1447 or write to lascience@lanl.gov by electronic mail.
--Steve Sandoval
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