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Displaying 1 - 25 of 154

From the Mise-en-pratique for Mass to the Future of Metrology for the SI

December 1, 2017
Author(s)
Carl J. Williams
The two most troublesome issues with the SI as currently defined involve the artifact kilogram (kg) and the electrical units. Defining the kg as exactly equal to the mass of the International Prototype Kilogram (IPK) poses severe difficulties in scaling

The Future of Quantum Based Measurements and the SI

December 1, 2017
Author(s)
Carl J. Williams
The U.S. National Institute of Standards and Technology (NIST), along with other NMIs, is preparing for a new era in the history of metrology made possible by the growing use of quantum-based standards and measurements. This development will dramatically

The SI and Quantum Metrology

December 1, 2017
Author(s)
Carl J. Williams
The United States’ National Institute of Standards and Technology (NIST) is playing a major role in the worldwide effort to base the International System of Units (SI) on fundamental constants. In many cases, units will be redefined in terms of invariant

Measurement of the Planck constant at the National Institute of Standards and Technology from 2015 to 2017

July 28, 2017
Author(s)
Darine El Haddad, Frank Seifert, Leon Chao, Antonio Possolo, David B. Newell, Jon R. Pratt, Carl J. Williams, Stephan Schlamminger
Researchers at the National Institute of Standards and Technology(NIST) estimate the value of the Planck constant as h = 6.62606994(10) x 10^-34 Js, hence with relative standard uncertainty 15.3 x 10^-9. This measurement result is based on over 17,000

Bridging classical and quantum mechanics

September 28, 2016
Author(s)
Darine El Haddad, Frank C. Seifert, Leon S. Chao, Shisong Lee, David B. Newell, Jon R. Pratt, Carl J. Williams, Stephan Schlamminger
Using a watt balance and a frequency comb, a mass-energy equivalence is derived. The watt balance compares mechanical power measured in terms of the meter, the second, and the kilogram to electrical power measured in terms of the volt and the ohm. A direct

A precise instrument to determine the Planck constant, and the future kilogram

June 21, 2016
Author(s)
Darine El Haddad, Frank C. Seifert, Leon S. Chao, David B. Newell, Jon R. Pratt, Carl J. Williams, Stephan Schlamminger, Shisong Li
A precise instrument, called a watt balance, compares mechanical power measured in terms of the meter, the second and the kilogram to electrical power measured in terms of the volt and the ohm. A direct link between mechanical action and the Planck

Chern Numbers Hiding in Time-of-Flight Images

December 21, 2011
Author(s)
Ian B. Spielman, Erhai Zhao, Noah Bray-Ali, Carl J. Williams, Indubala Satija
We present a novel technique for detecting topological invariants -- Chern numbers -- from time-of-flight images of ultra-cold neutral atoms. The Chern number of fermions in a lattice potential depends on magnetic field (for neutral atoms, generated by an

Detecting Paired and Counterflow superfluidity via dipole oscillations

October 27, 2011
Author(s)
Anzi A. Hu, Ludwig G. Mathey, Eite Tiesinga, Ippei Danshita, Carl J. Williams, Charles W. Clark
We suggest an experimentally feasible procedure to observe paired and counterflow superfluidity in ultra-cold atom systems. We study the time evolution of one-dimensional mixtures of bosonic atoms in an optical lattice following an abrupt displacement of

Effective three-body interactions of neutral atoms in optical lattices

September 15, 2009
Author(s)
Philip Johnson, Eite Tiesinga, James V. Porto, Carl J. Williams
We show that virtual excitations of neutral bosons to higher vibrational states in a three dimensional optical lattice generate effective, tunable, attractive three-body interactions. These effective processes can quickly decohere coherent states held in

Counterflow and paired superfluidity in one-dimensional Bose mixtures in optical lattices

August 24, 2009
Author(s)
Anzi A. Hu, Ludwig G. Mathey, Ippei Danshita, Eite Tiesinga, Carl J. Williams, Charles W. Clark
We study the quantum phases of mixtures of ultra-cold bosonic atoms held in an optical lattice that confines motion or hopping to one spatial dimension. The phases are found by using Tomonaga-Luttinger liquid theory as well as the numerical method of time

Experimental Study of High Speed Polarization -Coding Quantum Key Distribution with Sifted -Key Rates Over Mbit/s

June 1, 2009
Author(s)
Xiao Tang, Lijun Ma, Alan Mink, Anastase Nakassis, Barry J. Hershman, Joshua C. Bienfang, David H. Su, Ronald F. Boisvert, Charles W. Clark, Carl J. Williams
We have demonstrated a polarization encoded, fiber-based quantum key distribution system operating at 850 nm in the B92 protocol. With a quantum bit transmission rate i.e. optical pulse driving frequency of 625 MHz and a mean photon number of 0.1, we

Is Quantum Cryptography Provably Secure?

June 1, 2009
Author(s)
Anastase Nakassis, Joshua C. Bienfang, Paul M. Johnson, Alan Mink, D J. Rogers, Xiao Tang, Carl J. Williams
Quantum cryptography asserts that shared secrets can be established over public channels in such a way that the total information of an eavesdropper can be made arbitrarily small with probability arbitrarily close to 1. As we will show below, the current

Quantum Key Distribution System Operating at Sifted-Key Rate Over 4 Mbit/s 1

June 1, 2009
Author(s)
Xiao Tang, Lijun Ma, Alan Mink, Anastase Nakassis, Hai Xu, Barry J. Hershman, Joshua C. Bienfang, David H. Su, Ronald F. Boisvert, Charles W. Clark, Carl J. Williams
A complete fiber-based polarization encoding quantum key distribution (QKD) system based on the BB84 protocol has been developed at National Institute of Standard and Technology (NIST). The system can be operated at a sifted key rate of more than 4 Mbit/s

Perfect Quantum State Transfer With Superconducting Phase Qubits

October 16, 2008
Author(s)
Frederick Strauch, Carl J. Williams
Superconducting quantum circuits, fabricated with multiple layers, are proposed to implement perfect quantum state transfer between nodes of a hypercube network. For tunable devices such as the phase qubit, each node can transmit quantum information to any

Vortices, Antivortices and Superfluid Shells Separating Mott-Insulating Regions

October 16, 2008
Author(s)
Kaushik Mitra, Carl J. Williams, Carlos Sa de Melo
Atomic or molecular bosons in harmonically confined optical lattices are found to exhibit a wedding cake structure consisting of insulating (Mott) and superfluid shells. It is found that the order parameter equation in the superfluid regions is not of the

Population-imbalanced fermions in harmonically trapped optical lattices

July 21, 2008
Author(s)
Menderes Iskin, Carl J. Williams
The attractive Fermi-Hubbard Hamiltonian is solved via the Bogoliubov-de Gennes formalism to analyze the ground state phases of population imbalanced fermion mixtures in harmonically trapped two-dimensional optical lattices. In the low density limit the

Pseudo-Fermionization of 1-D Bosons in Optical Lattices

February 2, 2008
Author(s)
G Pupillo, A M. Rey, Carl J. Williams, Charles W. Clark
We present a model that generalizes the Bose-Fermi mapping for strongly correlated 1D bosons in an optical lattice, to cases in which the average number of atoms per site is larger than one. This model gives an accurate account of equilibrium properties of

Trap-Imbalanced Fermion Mixtures

January 7, 2008
Author(s)
Menderes Iskin, Carl J. Williams
We analyze the ground state phases of two-component population- andmass-balanced but trap-imbalanced fermion mixtures as a function of interactionstrength from the weak attraction Bardeen-Cooper-Schrieffer (BCS) to the strongattraction Bose-Einstein

Manipulation of the Collisional Frequency Shift in Caesium Fountain Clocks

September 13, 2007
Author(s)
K Szymaniec, W Chalupczak, S Weyers, R. Wynands, Eite Tiesinga, Carl J. Williams
The frequency shift due to atomic collisions is a major, and in some cases the dominant, limitation to the accuracy of caesium fountain primary frequency standards. A correction for this shift is usually obtained by measuring the frequency of the standard

Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks

April 13, 2007
Author(s)
K Szymaniec, W Chalupczak, Eite Tiesinga, Carl J. Williams, S Weyers, R. Wynands
We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F = 4, mF = 0> atoms, depending on the initial cloud

Demonstration of an Active Quantum Key Distribution Network

August 1, 2006
Author(s)
Xiao Tang, Lijun Ma, Alan Mink, Anastase Nakassis, Hai Xu, Barry J. Hershman, Joshua Bienfang, David H. Su, Ronald Boisvert, Charles W. Clark, Carl J. Williams
We previously demonstrated a high speed, point to point, quantum key distribution (QKD) system with polariztion coding over a fiber link, in which the resulting cryptographic keys were used for one-time pad encryption of real time video signals. In this

Quantum Key Distribution System Operating at Sifted-Key Rate over 4 Mbit/s

June 19, 2006
Author(s)
Xiao Tang, Lijun Ma, Alan Mink, Anastase Nakassis, Hai Xu, Barry J. Hershman, Joshua Bienfang, David H. Su, Ronald Boisvert, Charles W. Clark, Carl J. Williams
A complete fiber-based polarization encoding quantum key distribution (QKD) system based on the BB84 protocol has been developed at National Institute of Standard and Technology (NIST). The system can be operated at a sifted key rate of more than 4 Mbit/s