Charles Clark | National Institute of Standards and Technology (original) (raw)
Papers by Charles Clark
Optics and Photonics News, 2013
Nonlinear optics has come a long way since the laser. This article reviews recent progress in coh... more Nonlinear optics has come a long way since the laser. This article reviews recent progress in coherent wave mixing and introduces some new concepts that will reframe future research directions.
Physics Today, 2013
The consequences, for good and ill, of that annus mirabilis of discovery and invention are still ... more The consequences, for good and ill, of that annus mirabilis of discovery and invention are still very much with us.
Physical Review Letters, 1999
We discuss collective excitations of a trapped dilute Fermi gas within a hydrodynamic approximati... more We discuss collective excitations of a trapped dilute Fermi gas within a hydrodynamic approximation. Analytical results are derived for both high-and low-temperature limits and are applied to 40 K and 6 Li systems of current experimental interest. We identify spectral signatures which can be used to detect the onset of Fermi degeneracy. Also, we find an interesting class of internal excitations with an unusual spectrum. Some of our results are relevant to the case of trapped bosons as well. Our analysis suggests several experiments which address fundamental problems of collective motion in quantum fluids.
Physical Review Letters, 1998
ABSTRACT
Optics Express, 1997
For a dilute, interacting Bose gas of magnetically-trapped atoms at temperatures below the critic... more For a dilute, interacting Bose gas of magnetically-trapped atoms at temperatures below the critical temperature T 0 for Bose-Einstein condensation, we determine the second-order coherence function g (2) (r 1 , r 2) within the framework of a finite-temperature quantum field theory. We show that, because of the different spatial distributions of condensate and thermal atoms in the trap, g (2) (r 1 , r 2) does not depend on |r 1 − r 2 | alone. This means that the experimental determinations of g (2) reported to date give only its spatial average. Such an average may underestimate the degree of coherence attainable in an atom laser by judicious engineering of the output coupler.
We present a finite temperature kinetic theory for a dilute, trapped Bose-condensed gas of two-le... more We present a finite temperature kinetic theory for a dilute, trapped Bose-condensed gas of two-level atoms. This spin-1/2 system exhibits interesting collective effects in the spin dynamics. Above T_c, the gas supports spin wave collective modes due to the Hartree-Fock exchange mean field, which have been observed in recent experiments at JILA. In the opposite limit of T=0, interesting effects have also been observed in the spin-1/2 condensate at JILA, such as spin "untwisting" and vortex spin textures. We give a unified picture of these two situations and discuss possible new physics that occurs below Tc where the spins of the condensate and thermal atoms interact through mean field and collisional processes.
The next generation of quantum cryptography will benefit from a fast and practical source of enta... more The next generation of quantum cryptography will benefit from a fast and practical source of entangled photon pairs. Current methods of generating entanglement, whether in bulk nonlinear crystals or microstructure optical fibers, pose significant challenges to integration into fieldable quantum communications systems. In order to meet the demands of speed and practicality, we investigate third-order nonlinearity in a semiconductor waveguide as a source of correlated and ultimately entangled photon pairs. This device offers the advantages of a fast nonlinear response based on the optical Kerr effect and the relative ease of coupling to standard optical fibers. It is potentially useful for free-space and fiber-optic quantum key distribution as well as a host of other applications such as correlated photon metrology and two-photon interferometry. We show the feasibility of using phase-matched four-wave mixing in a birefringent AlGaAs waveguide to generate correlated photon pairs at wavelengths compatible with silicon detectors. We demonstrate the operation of such a device, consider the effects of loss and two-photon absorption, and evaluate the implications of birefringent phase matching.
Atoms, 2022
Recent atom interferometry (AI) experiments involving Bose–Einstein condensates (BECs) have been ... more Recent atom interferometry (AI) experiments involving Bose–Einstein condensates (BECs) have been conducted under extreme conditions of volume and interrogation time. Numerical solution of the rotating-frame Gross–Pitaevskii equation (RFGPE), which is the standard mean-field theory applied to these experiments, is impractical due to the excessive computation time and memory required. We present a variational model that provides approximate solutions of the RFGPE for a power-law potential on a practical time scale. This model is well-suited to the design and analysis of AI experiments involving BECs that are split and later recombined to form an interference pattern. We derive the equations of motion of the variational parameters for this model and illustrate how the model can be applied to the sequence of steps in a recent AI experiment where BECs were used to implement a dual-Sagnac atom interferometer rotation sensor. We use this model to investigate the impact of finite-size and i...
Physical review letters, Jan 17, 2015
In nonrelativistic quantum theories with short-range Hamiltonians, a velocity v can be chosen suc... more In nonrelativistic quantum theories with short-range Hamiltonians, a velocity v can be chosen such that the influence of any local perturbation is approximately confined to within a distance r until a time t∼r/v, thereby defining a linear light cone and giving rise to an emergent notion of locality. In systems with power-law (1/r^{α}) interactions, when α exceeds the dimension D, an analogous bound confines influences to within a distance r only until a time t∼(α/v)logr, suggesting that the velocity, as calculated from the slope of the light cone, may grow exponentially in time. We rule out this possibility; light cones of power-law interacting systems are bounded by a polynomial for α>2D and become linear as α→∞. Our results impose strong new constraints on the growth of correlations and the production of entangled states in a variety of rapidly emerging, long-range interacting atomic, molecular, and optical systems.
Review of Scientific Instruments, 2002
The National Institute of Standards and Technology ͑NIST͒ has operated the Synchrotron Ultraviole... more The National Institute of Standards and Technology ͑NIST͒ has operated the Synchrotron Ultraviolet Radiation Facility ͑SURF͒ continuously since the early 1960s. The original accelerator was converted into a storage ring, called SURF II, in 1974. Then in 1998, motivated mainly by limitations in the accuracy of radiometric calibrations and the wish to extend the spectrum of the emitted synchrotron radiation to shorter wavelengths, a second major upgrade was performed. This time the whole magnet system was replaced to improve the calculability and allow for higher magnetic fields. Since the recommissioning of SURF III we have been working to improve the stability of the stored electron beam through modifications of the radio-frequency system, leading to operations with unprecedented stability and new record injection currents topping 700 mA.
The Journal of Chemical Physics, 2014
Physical Review A, 1997
Erratum: Local-density-functional calculations of the energy of atoms [Phys. Rev. A 55, 191 (1997... more Erratum: Local-density-functional calculations of the energy of atoms [Phys. Rev. A 55, 191 (1997)]. ...
Physical Review A, 1998
A hydrodynamical version of the time-dependent Gross-Pitaevskii equation has been formulated and ... more A hydrodynamical version of the time-dependent Gross-Pitaevskii equation has been formulated and applied to the description of a Bose-Einstein condensate ͑BEC͒ of 87 Rb atoms in the JILA time-averaged orbiting potential ͑TOP͒ trap. The response of the BEC to time-dependent modulations of the trap potential is computed and the characteristic frequencies of a BEC oscillation agree well with those observed in recent experiments. For the axially symmetric mϭ0 mode of the TOP trap, we find a weak dependence of the oscillatory frequency on the strength of the driving amplitude under conditions comparable to those of current experiments. The free ringing of the BEC that is induced by a transient change in the potential is found to be periodic, in agreement with the predictions of Thomas-Fermi theory. We analyze the harmonic content of the spectral response and consider possibilities for high-harmonic generation in the context of nonlinear atom optics.
Optics Express, 2010
Two hundred eighty three uniaxial ellipsoids with sizes from 4 mm to 11 mm were measured with a c... more Two hundred eighty three uniaxial ellipsoids with sizes from 4 mm to 11 mm were measured with a coordinate measuring matching (CMM) and also scanned using a medical computed tomography (CT) machine. Their volumes were determined by counting voxels over a threshold, as well as using equivalent volumes from the length given by the RECIST 1.1 criterion (Response Evaluation Criteria in Solid Tumors). The volumetric measurements yield an order of magnitude reduction in residuals compared to the CMM measurements than the residuals of the RECIST measurements also compared to the CMM measurements.
In some of the first applications of modern quantum mechanics to the spectroscopy of many-electro... more In some of the first applications of modern quantum mechanics to the spectroscopy of many-electron atoms, Ettore Majorana solved several outstanding problems by developing the theory of autoionization. Later literature makes only sporadic references to this accomplishment. After reviewing his work in its contemporary context, we describe subsequent developments in understanding the spectra treated by Majorana, and extensions of his theory to other areas of physics. We find many puzzles concerning the way in which the modern theory of autoionization was developed. ∗ Permanent address: Dipartimento di Fisica E. Fermi, Università di Pisa, Italy †Electronic address: arimondo@df.unipi.it ‡Electronic address: clark@nist.gov §Electronic address: wmartin@nist.gov
Optics and Photonics News, 2013
Nonlinear optics has come a long way since the laser. This article reviews recent progress in coh... more Nonlinear optics has come a long way since the laser. This article reviews recent progress in coherent wave mixing and introduces some new concepts that will reframe future research directions.
Physics Today, 2013
The consequences, for good and ill, of that annus mirabilis of discovery and invention are still ... more The consequences, for good and ill, of that annus mirabilis of discovery and invention are still very much with us.
Physical Review Letters, 1999
We discuss collective excitations of a trapped dilute Fermi gas within a hydrodynamic approximati... more We discuss collective excitations of a trapped dilute Fermi gas within a hydrodynamic approximation. Analytical results are derived for both high-and low-temperature limits and are applied to 40 K and 6 Li systems of current experimental interest. We identify spectral signatures which can be used to detect the onset of Fermi degeneracy. Also, we find an interesting class of internal excitations with an unusual spectrum. Some of our results are relevant to the case of trapped bosons as well. Our analysis suggests several experiments which address fundamental problems of collective motion in quantum fluids.
Physical Review Letters, 1998
ABSTRACT
Optics Express, 1997
For a dilute, interacting Bose gas of magnetically-trapped atoms at temperatures below the critic... more For a dilute, interacting Bose gas of magnetically-trapped atoms at temperatures below the critical temperature T 0 for Bose-Einstein condensation, we determine the second-order coherence function g (2) (r 1 , r 2) within the framework of a finite-temperature quantum field theory. We show that, because of the different spatial distributions of condensate and thermal atoms in the trap, g (2) (r 1 , r 2) does not depend on |r 1 − r 2 | alone. This means that the experimental determinations of g (2) reported to date give only its spatial average. Such an average may underestimate the degree of coherence attainable in an atom laser by judicious engineering of the output coupler.
We present a finite temperature kinetic theory for a dilute, trapped Bose-condensed gas of two-le... more We present a finite temperature kinetic theory for a dilute, trapped Bose-condensed gas of two-level atoms. This spin-1/2 system exhibits interesting collective effects in the spin dynamics. Above T_c, the gas supports spin wave collective modes due to the Hartree-Fock exchange mean field, which have been observed in recent experiments at JILA. In the opposite limit of T=0, interesting effects have also been observed in the spin-1/2 condensate at JILA, such as spin "untwisting" and vortex spin textures. We give a unified picture of these two situations and discuss possible new physics that occurs below Tc where the spins of the condensate and thermal atoms interact through mean field and collisional processes.
The next generation of quantum cryptography will benefit from a fast and practical source of enta... more The next generation of quantum cryptography will benefit from a fast and practical source of entangled photon pairs. Current methods of generating entanglement, whether in bulk nonlinear crystals or microstructure optical fibers, pose significant challenges to integration into fieldable quantum communications systems. In order to meet the demands of speed and practicality, we investigate third-order nonlinearity in a semiconductor waveguide as a source of correlated and ultimately entangled photon pairs. This device offers the advantages of a fast nonlinear response based on the optical Kerr effect and the relative ease of coupling to standard optical fibers. It is potentially useful for free-space and fiber-optic quantum key distribution as well as a host of other applications such as correlated photon metrology and two-photon interferometry. We show the feasibility of using phase-matched four-wave mixing in a birefringent AlGaAs waveguide to generate correlated photon pairs at wavelengths compatible with silicon detectors. We demonstrate the operation of such a device, consider the effects of loss and two-photon absorption, and evaluate the implications of birefringent phase matching.
Atoms, 2022
Recent atom interferometry (AI) experiments involving Bose–Einstein condensates (BECs) have been ... more Recent atom interferometry (AI) experiments involving Bose–Einstein condensates (BECs) have been conducted under extreme conditions of volume and interrogation time. Numerical solution of the rotating-frame Gross–Pitaevskii equation (RFGPE), which is the standard mean-field theory applied to these experiments, is impractical due to the excessive computation time and memory required. We present a variational model that provides approximate solutions of the RFGPE for a power-law potential on a practical time scale. This model is well-suited to the design and analysis of AI experiments involving BECs that are split and later recombined to form an interference pattern. We derive the equations of motion of the variational parameters for this model and illustrate how the model can be applied to the sequence of steps in a recent AI experiment where BECs were used to implement a dual-Sagnac atom interferometer rotation sensor. We use this model to investigate the impact of finite-size and i...
Physical review letters, Jan 17, 2015
In nonrelativistic quantum theories with short-range Hamiltonians, a velocity v can be chosen suc... more In nonrelativistic quantum theories with short-range Hamiltonians, a velocity v can be chosen such that the influence of any local perturbation is approximately confined to within a distance r until a time t∼r/v, thereby defining a linear light cone and giving rise to an emergent notion of locality. In systems with power-law (1/r^{α}) interactions, when α exceeds the dimension D, an analogous bound confines influences to within a distance r only until a time t∼(α/v)logr, suggesting that the velocity, as calculated from the slope of the light cone, may grow exponentially in time. We rule out this possibility; light cones of power-law interacting systems are bounded by a polynomial for α>2D and become linear as α→∞. Our results impose strong new constraints on the growth of correlations and the production of entangled states in a variety of rapidly emerging, long-range interacting atomic, molecular, and optical systems.
Review of Scientific Instruments, 2002
The National Institute of Standards and Technology ͑NIST͒ has operated the Synchrotron Ultraviole... more The National Institute of Standards and Technology ͑NIST͒ has operated the Synchrotron Ultraviolet Radiation Facility ͑SURF͒ continuously since the early 1960s. The original accelerator was converted into a storage ring, called SURF II, in 1974. Then in 1998, motivated mainly by limitations in the accuracy of radiometric calibrations and the wish to extend the spectrum of the emitted synchrotron radiation to shorter wavelengths, a second major upgrade was performed. This time the whole magnet system was replaced to improve the calculability and allow for higher magnetic fields. Since the recommissioning of SURF III we have been working to improve the stability of the stored electron beam through modifications of the radio-frequency system, leading to operations with unprecedented stability and new record injection currents topping 700 mA.
The Journal of Chemical Physics, 2014
Physical Review A, 1997
Erratum: Local-density-functional calculations of the energy of atoms [Phys. Rev. A 55, 191 (1997... more Erratum: Local-density-functional calculations of the energy of atoms [Phys. Rev. A 55, 191 (1997)]. ...
Physical Review A, 1998
A hydrodynamical version of the time-dependent Gross-Pitaevskii equation has been formulated and ... more A hydrodynamical version of the time-dependent Gross-Pitaevskii equation has been formulated and applied to the description of a Bose-Einstein condensate ͑BEC͒ of 87 Rb atoms in the JILA time-averaged orbiting potential ͑TOP͒ trap. The response of the BEC to time-dependent modulations of the trap potential is computed and the characteristic frequencies of a BEC oscillation agree well with those observed in recent experiments. For the axially symmetric mϭ0 mode of the TOP trap, we find a weak dependence of the oscillatory frequency on the strength of the driving amplitude under conditions comparable to those of current experiments. The free ringing of the BEC that is induced by a transient change in the potential is found to be periodic, in agreement with the predictions of Thomas-Fermi theory. We analyze the harmonic content of the spectral response and consider possibilities for high-harmonic generation in the context of nonlinear atom optics.
Optics Express, 2010
Two hundred eighty three uniaxial ellipsoids with sizes from 4 mm to 11 mm were measured with a c... more Two hundred eighty three uniaxial ellipsoids with sizes from 4 mm to 11 mm were measured with a coordinate measuring matching (CMM) and also scanned using a medical computed tomography (CT) machine. Their volumes were determined by counting voxels over a threshold, as well as using equivalent volumes from the length given by the RECIST 1.1 criterion (Response Evaluation Criteria in Solid Tumors). The volumetric measurements yield an order of magnitude reduction in residuals compared to the CMM measurements than the residuals of the RECIST measurements also compared to the CMM measurements.
In some of the first applications of modern quantum mechanics to the spectroscopy of many-electro... more In some of the first applications of modern quantum mechanics to the spectroscopy of many-electron atoms, Ettore Majorana solved several outstanding problems by developing the theory of autoionization. Later literature makes only sporadic references to this accomplishment. After reviewing his work in its contemporary context, we describe subsequent developments in understanding the spectra treated by Majorana, and extensions of his theory to other areas of physics. We find many puzzles concerning the way in which the modern theory of autoionization was developed. ∗ Permanent address: Dipartimento di Fisica E. Fermi, Università di Pisa, Italy †Electronic address: arimondo@df.unipi.it ‡Electronic address: clark@nist.gov §Electronic address: wmartin@nist.gov