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Search Publications by: Emanuel Knill (Fed)

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Displaying 26 - 50 of 90

Analysis of coincidence-time loopholes in experimental Bell tests

March 4, 2015
Author(s)
B. G. Christensen, A. Hill, P. G. Kwiat, Emanuel Knill, Sae Woo Nam, Kevin Coakley, Scott Glancy, Krister Shalm, Y. Zhang
We apply a distance-based Bell-test analysis method ["Bell inequalities for continuously emitting sources" E. Knill et al. arXiv:14097732 (2014)] to three experimental data sets where conventional analyses failed or required additional assumptions. The

Bell Inequalities for Continuously Emitting Sources

March 4, 2015
Author(s)
Emanuel H. Knill, Scott C. Glancy, Sae Woo Nam, Kevin J. Coakley, Yanbao Zhang
A common experimental strategy for demonstrating non-classical correlations is to show violation of a Bell inequality by measuring a continuously emitted stream of entangled photon pairs. The measurements involve the detection of photons by two spatially

Optimizing Passive Quantum Clocks

October 8, 2014
Author(s)
Michael J. Mullan, Emanuel Knill
We describe protocols for passive atomic clocks based onquantum interrogation of the atoms. Unlike previous techniques, our protocols are adaptive and take advantage of prior information about the clock's state. To reduce deviations from an ideal clock

Tunable spin-spin interactions and entanglement of ions in separate controlled potential wells

August 7, 2014
Author(s)
Andrew C. Wilson, Yves Colombe, K. R. Brown, Emanuel H. Knill, Dietrich G. Leibfried, David J. Wineland
Inspired by the ideas of Richard Feynman, 1 David Deutsch, 2 Seth Lloyd 3 and others, researchers in the field of quantum information processing and simulation seek to harness the quantum-mechanical properties of well-controlled laboratory systems to

Efficient quantification of experimental evidence against local realism

November 18, 2013
Author(s)
Yanbao Zhang, Scott C. Glancy, Emanuel H. Knill
To statistically quantify the evidence against local realism in an experiment, it is desirable to bound the probability according to local realism of a violation at least as high as that observed. We describe an efficient protocol for computing such a

Building Quantum Computers

January 22, 2013
Author(s)
Emanuel H. Knill
Abstract: In theory, quantum computers can be used to efficiently factor numbers, quadratically speed up many search and optimization problems, and enable currently impossible physics simulations. At first, quantum states appeared to be too fragile for

Gradient-based stopping rules for maximum-likelihood quantum-state tomography

September 18, 2012
Author(s)
Scott C. Glancy, Emanuel H. Knill, Mark Girard
When performing maximum likelihood quantum state tomography, one must find the quantum state that maximizes the likelihood for observed measurements on identically prepared systems, all having that quantum state. This optimization is usually performed with

Improving Quantum Clocks via Semidefinite Programming

July 26, 2012
Author(s)
Michael J. Mullan, Emanuel H. Knill
The accuracies of modern quantum logic clocks have surpassed those of standard atomic fountain clocks. These clocks also provide a greater degree of control, as before and after clock queries, we are able to apply chosen unitary operations and measurements

Randomized Benchmarking of Multiqubit Gates

June 29, 2012
Author(s)
John P. Gaebler, Adam M. Meier, Ting Rei Tan, Ryan S. Bowler, Yiheng Lin, David Hanneke, John D. Jost, Jonathan Home, Emanuel H. Knill, Dietrich G. Leibfried, David J. Wineland
As experimental platforms for quantum information processing continue to mature, characterization of the quality of unitary gates that can be applied to their quantum bits (qubits) becomes essential. Eventually, the quality must be sufficiently high to

The non-Abelian Duality Problem

June 6, 2012
Author(s)
Emanuel H. Knill, E. Cobanera, Gerardo Ortiz
We exploit a new theory of duality transformations to construct dual representations of models incompatible with traditional duality transformations. Hence we obtain a solution to the long-standing problem of non-Abelian dualities that hinges on two key

Magic-state distillation with the four-qubit code

April 20, 2012
Author(s)
Adam M. Meier, Bryan K. Eastin, Emanuel H. Knill
The distillation of magic states is an often-cited technique for enabling universal quantum computing once the error rate for a special subset of gates has been made negligible by other means. We present a routine for magic-state distillation that reduces

Asymptotically Optimal Confidences for Rejecting Local Realism

December 22, 2011
Author(s)
Yanbao Zhang, Scott Glancy, Emanuel Knill
Reliable experimental demonstrations of violations of local realism are highly desirable for fundamental tests of Quantum Mechanics. Such violations can be quantified in terms of a confidence for rejecting local realism. We propose a method for computing

Generation and characterization of high-purity, pulsed squeezed light at telecom wavelengths from pp-KTP

November 15, 2011
Author(s)
Thomas Gerrits, Martin J. Stevens, Burm Baek, Brice R. Calkins, Adriana E. Lita, Scott C. Glancy, Emanuel H. Knill, Sae Woo Nam, Richard P. Mirin, Robert Hadfield, Ryan Bennink, Warren Grice, Sander N. Dorenbos, Tony Zijlstra, Teun Klapwijk, Val Zwiller
We characterize a pp-KTP crystal designed to produce pure single mode squeezed vacuum at 1570 nm. Measurements show a raw (corrected) Hong-Ou-Mandel interference with 86 % (90 %) visibility and a circular joint spectral probability distribution with a

Single-qubit-gate error below 10 -4 in a trapped ion

September 14, 2011
Author(s)
Kenton R. Brown, Andrew C. Wilson, Yves Colombe, Christian Ospeklaus, Adam M. Meier, Emanuel H. Knill, Dietrich G. Leibfried, David J. Wineland
In theory, quantum computers can solve certain problems much more efficiently than classical computers [1]. This has motivated experimental efforts to construct and verify devices that manipulate quantum bits (qubits) in a variety of physical systems [2]

Characterization of high-purity, pulsed squeezed light at telecom wavelengths from pp-KTP for quantum information applications

May 1, 2011
Author(s)
Thomas Gerrits, Burm Baek, Martin J. Stevens, Brice R. Calkins, Adriana E. Lita, Scott C. Glancy, Emanuel H. Knill, Sae Woo Nam, Richard P. Mirin, Robert Hadfield, Ryan Bennink, Warren Grice, Sander N. Dorenbos, Tony Zijlstra, Teun Klapwijk, Val Zwiller
We characterize a pp-KTP crystal designed to produce pure single mode squeezed vacuum at 1570 nm. Measurements show Hong-Ou-Mandel interference with 97% visibility and a circular joint spectral distribution with a Schmidt number of 1.08.

Characterization of high-purity, pulsed squeezed light at telecom wavelengths from pp-KTP for quantum information applications

December 1, 2010
Author(s)
Thomas Gerrits, Burm Baek, Martin J. Stevens, Brice R. Calkins, Adriana E. Lita, Scott C. Glancy, Emanuel H. Knill, Sae Woo Nam, Richard P. Mirin, Robert Hadfield, Ryan Bennink, Warren Grice, Sander N. Dorenbos, Tony Zijlstra, Teun Klapwijk, Val Zwiller
Pure optical squeezing in a single mode is highly desirable for quantum information applications such as continuous variable quantum computing and the generation of optical Schrödinger cat states. To generate optical cat states, photons are subtracted from

Generation of optical coherent-state superpositions by number-resolved photon subtraction from the squeezed vacuum

September 9, 2010
Author(s)
Thomas Gerrits, Scott C. Glancy, Tracy S. Clement, Brice R. Calkins, Adriana E. Lita, Aaron Miller, Aaron J. Miller, Alan L. Migdall, Sae Woo Nam, Richard P. Mirin, Emanuel H. Knill
We have created heralded coherent-state superpositions (CSSs) by subtracting up to three photons from a pulse of squeezed vacuum light. To produce such CSSs at a sufficient rate, we used our high-efficiency photon-number-resolving transition edge sensor to

Generation of optical Schrodinger cat states by number-resolved squeezed photon subtraction

July 23, 2010
Author(s)
Thomas Gerrits, Scott C. Glancy, Tracy S. Clement, Brice R. Calkins, Adriana E. Lita, Aaron J. Miller, Alan L. Migdall, Aaron J. Miller, Sae Woo Nam, Richard P. Mirin, Emanuel H. Knill
We have generated and measured an approximation of an optical Schrödinger cat state by photon subtraction from squeezed vacuum. Figure 1 shows the experimental scheme. Photons are probabilistically subtracted from squeezed vacuum and detected with a photon

Fast Quantum Algorithms for Traversing Paths of Eigenstates

May 17, 2010
Author(s)
S. Boixo, Emanuel Knill, Rolando Somma
Consider a path of non-degenerate eigenstates |psi_s>, 0 Solutions to this problem have applications ranging from quantum physics simulation to optimization. For Hamiltonians, the conventional way of doing this is by applying the adiabatic theorem. We give

Quantum Computing

January 28, 2010
Author(s)
Emanuel H. Knill
Imagine a computer that can exploit quantum mechanics to solve previously intractable problems in physics, mathematics and cryptography. Such a quantum computer would revolutionize computing technology while teaching us about fundamental physics and ways

Innovations in Maximum Likelihood Quantum State Tomography

October 9, 2009
Author(s)
Scott C. Glancy, Emanuel H. Knill, Thomas Gerrits, Tracy S. Clement, Brice R. Calkins, Adriana E. Lita, Aaron J. Miller, Alan L. Migdall, Sae Woo Nam, Richard P. Mirin
At NIST we are engaged in an experiment whose goal is to create superpositions of optical coherent states (such superpositions are sometimes called "Schroedinger cat" states). We use homodyne detection to measure the light, and we apply maximum likelihood

Eigenpath Traversal by Phase Randomization

September 1, 2009
Author(s)
S. Boixo, Emanuel Knill, Rolando Somma
A computation in adiabatic quantum computing is achieved by traversing a path of nondegenerate eigenstates of a continuous family of Hamiltonians. We introduce a method that traverses a discretized form of the path: at each step we evolve with the

Generation of optical Schrodinger cat states by number-resolved squeezed photon subtraction

May 31, 2009
Author(s)
Thomas Gerrits, Scott C. Glancy, Tracy S. Clement, Brice R. Calkins, Adriana E. Lita, Aaron J. Miller, Alan L. Migdall, Sae Woo Nam, Richard P. Mirin, Emanuel H. Knill
We have generated and measured an approximation of an optical Schrödinger cat state by photon subtraction from a squeezed state. Using single-photon avalanche photodiode detectors and photon-number-resolving transition edge sensors, we were able to extract

Restrictions on Transversal Encoded Quantum Gate Sets

March 18, 2009
Author(s)
Bryan K. Eastin, Emanuel H. Knill
Transversal gates play an important role in the theory of fault-tolerant quantum computation due to their simplicity and robustness to noise. By definition, transversal operators do not couple physical subsystems within the same code block. Consequently