Previous session | Next session Session E5 - Atomic, Molecular and Optical Physics Thesis Award. INVITED session, Thursday morning, May 28 Mesa Ballroom, Hilton [E5.01] Impossibility of Determining the Quantum Wavefunction of a Single System and Fundamental Limit to External Force Detection Orly Alter (ERATO Quantum Fluctuation Project, Stanford University) Technology has advanced to the point that single quantum systems can now be controlled. Due to these advances, fundamental questions in quantum theory are being faced in laboratories all over the world. The possibility of performing a series of measurements on a single quantum system has renewed interest in the question of the physical reality of the wavefunction: what is the fundamental limit to the determination of the quantum wavefunction of a single system? Recently, Aharonov et. al. suggested that it may be possible to determine the unknown quantum wavefunction of a single system. State-of-the-art precision measurements, which are based on the monitoring of the time evolution of a single physical system, has renewed interest in the question of the quantum Zeno effect of a single system: what is the fundamental limit to the determination of the time evolution of a single system? And to the detection of a classical signal via the monitoring of a single system? Braginsky et. al., Caves et. al. and Yuen suggested independently that there may be no limit to the detection of an external force via the monitoring of a single quantum harmonic oscillator. This dissertation establishes the quantum theoretical limits to the information which can be obtained in the measurement of a single system. We prove that information about the unknown quantum wavefunction of the system is limited to estimates of the expectation values of the measured observables, where the estimate errors satisfy the uncertainty principle. This is due to the reduction process: in a series of measurements of a single system, each measurement changes the wavefunction of the measured system in accordance with the measurement result, and therefore the statistics of each measurement result depend on the results of all the previous measurements. The quantum measurement which does not change the wavefunction of the measured system at all requires full a-priori knowledge of this wavefunction. We show that this impossibility of determining the quantum wavefunction of a single system and the quantum Zeno effect of a single system are equivalent. These effects impose a fundamental limit to precision measurement techniques. We show that in the detection of an external force via the monitoring of a single quantum harmonic oscillator, this limit requires an exchange of at least one quantum of energy between the force and the oscillator. [E5.02] Resonant Dipole-Dipole Collisions of Rydberg Atoms in a Magneto-Optical Trap W. R. Anderson (University of Virginia, Charlottesville, VA 22901) I present a study of resonant energy transfer via a dipole-dipole interaction between alkali atoms in Rydberg states. We have studied such interactions between atoms prepared in a magneto-optical trap (MOT). In binary collisions the atomic density plays no role in the collision dynamics, however, using laser cooling and trapping techniques we have been able to enter a new regime for resonant energy transfer. In this regime the resonance widths are described by a model in which the atoms are ``frozen'' in place during a collision. We also exploit the long interaction times of the cold atoms in a MOT to observe Ramsey interference fringes in resonant energy transfer between rubidium atoms. A manifestation of electromagnetically induced transparency in potassium Rydberg atom collisions is also presented. [E5.03] Bose-Einstein condensation in atomic alkali gases Robert J. Dodd (Department of Physics, Oxford University, United Kingdom) I present a review of the time-independent Gross-Pitaevskii (GP), Bogoliubov, and finite-temperature Hartree-Fock-Bogoliubov (HFB) mean-field theories used to study trapped, Bose-Einstein condensed alkali gases. Numerical solutions of the (zero-temperature) GP equation are presented for attractive (negative scattering length) and repulsive (positive scattering length) interactions. Comparison is made with the Thomas-Fermi and (variational) trial wavefunction appr oximations that are used in the literature to study condensed gases. Numerical calculations of the (zero-temperature) Bogoliubov quasi-particle excitation frequencies are found to be in excellent agreement with the experimental results. The finite-temperature properties of condensed gases are examined using the Popov approximation (of the HFB theory) and a simple two-gas model. Specific, quantitative comparisons are made with experimental results for finite-temperature excitation frequencies. Qualitative comparisons are made between the results of the Popov approximation, two-gas model, and other published models for condensate fraction and thermal density distribution. The time-independent mean-field theories are found to be in excellent agreement with experimental results at relatively low temperatures (high condensate fractions). However, at higher temperatures (and condensate fractions of less than 50%) there are significant discrepancies between experimental data and theoretical calculations. This work was undertaken at the University of Maryland at College Park and was supported in part by the National Science Foundation (PHY-9601261) and the U.S. Office of Naval Research. [E5.04] Rydberg Wave Packets and Half-Cycle Electromagnetic Pulses Chandra S. Raman (Massachusetts Institute of Technology) This dissertation summarizes an examination of the dynamics of atomic Rydberg wave packets with coherent pulses of THz electromagnetic radiation consisting of less than a single cycle of the electric field. The bulk of the energy is contained in just a half-cycle. Previous work ( R.~Jones, D.~You, and P.~Bucksbaum, ``Ionization of Rydberg atoms by subpicosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~70, 1993. had shown how these half-cycle pulses can be used to ionize the highly excited states of an atom, and that a classical view of electronic motion in the atom explains the ionization mechanism. To further probe the boundary between classical trajectories and quantum mechanics, in this work I investigate dynamical combinations of Rydberg states, or Rydberg wave packets, and how they ionize under the influence of a half-cycle electromagnetic pulse. With time-domain techniques I am able to extract the dynamics of the wave packet from the ionization rate, and to observe wave packet motion in both the electronic radial ( C.~Raman, C.~Conover, C.~Sukenik, and P.~Bucksbaum, ``Ionization of Rydberg wavepackets by sub-picosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~76, 1996.and angular ( C.~Raman, T.~Weinacht, and P.~Bucksbaum, ``Stark wavepackets viewed with half cycle pulses.'' Phys. Rev. A), vol.~ 55, No. 6, 1997. coordinates. This is the first time a wavepacket technique has been used to view electron motion everywhere on its trajectory, and not just at the nucleus. This is the principal feature of half-cycle pulse ionization. Semiclassical ideas of ionization in conjunction with quantum descriptions of the wave packet, are capable of reproducing the main trends in the data, and in the absence of a rigorous model I rely on these. Experiments of this nature provide examples of the ongoing effort to use the coherent properties of radiation to control electronic motion in an atom, as well as to probe the boundaries between quantum and classical mechanics. [E5.05] Improved measurement of parity nonconservation in atomic cesium and first measurement of the nuclear anapole moment Chris Wood (JILA and University of Colorado, Boulder) Historically, atomic parity nonconservation (PNC) measurements have bridged the gap between high energy and low energy physics. Our recently completed 0.35% measurement of PNC in cesium(C. S. Wood extit et al., Science) extbf 275, 1759 (1997) has gone a step further and created a bridge between atomic physics and nuclear physics. This measurement represents the best low energy test of electroweak unification and, in addition, we have made a 14% measurement of the parity violating nuclear anapole moment(V.V. Flambaum extit et al., Phys. Lett. B) extbf 146, 367 (1984). Cesium continues to hold a special place for atomic PNC measurements due to the accuracy (1%) with which the necessary atomic structure calculations can be made(S.A. Blundell, J. Sapirstein, and W. R. Johnson, extit Phys. Rev. D) extbf 45, 1602 (1992); V.A. Dzuba, V. V. Flambaum, and O. P. Sushkov, Phys. Lett. A 141, 147 (1989)., and our result has motivated new calculations. The experiment uses a Stark interference technique to measure PNC, and has achieved a factor of seven improvement over our previous result. Two frequency-stabilized diode lasers are used to optically pump an intense cesium beam, while a third is used for detection and a fourth is used to monitor the spin polarization of the atomic beam using stimulated Raman transitions. A dye laser operating at 540nm, phase locked to a finesse 100,000 power buildup cavity, is used to excite the forbidden 6S-7S transition in a region of crossed electric and magnetic fields. These fields serve to define an experimental coordinate system. We have developed 5 different ways to parity transform this coordinate system, which are crucial to our ability to suppress systematic errors. Our signal is the interference of an allowed 6S-7S transition amplitude with the PNC transition amplitude, which causes a tiny (6 ppm) fractional modulation of the 6S-7S excitation rate synchronous with all 5 parity transformations. Previous session | Next session Session E5 - Atomic, Molecular and Optical Physics Thesis Award. INVITED session, Thursday morning, May 28 Mesa Ballroom, Hilton [E5.01] Impossibility of Determining the Quantum Wavefunction of a Single System and Fundamental Limit to External Force Detection Orly Alter (ERATO Quantum Fluctuation Project, Stanford University) Technology has advanced to the point that single quantum systems can now be controlled. Due to these advances, fundamental questions in quantum theory are being faced in laboratories all over the world. The possibility of performing a series of measurements on a single quantum system has renewed interest in the question of the physical reality of the wavefunction: what is the fundamental limit to the determination of the quantum wavefunction of a single system? Recently, Aharonov et. al. suggested that it may be possible to determine the unknown quantum wavefunction of a single system. State-of-the-art precision measurements, which are based on the monitoring of the time evolution of a single physical system, has renewed interest in the question of the quantum Zeno effect of a single system: what is the fundamental limit to the determination of the time evolution of a single system? And to the detection of a classical signal via the monitoring of a single system? Braginsky et. al., Caves et. al. and Yuen suggested independently that there may be no limit to the detection of an external force via the monitoring of a single quantum harmonic oscillator. This dissertation establishes the quantum theoretical limits to the information which can be obtained in the measurement of a single system. We prove that information about the unknown quantum wavefunction of the system is limited to estimates of the expectation values of the measured observables, where the estimate errors satisfy the uncertainty principle. This is due to the reduction process: in a series of measurements of a single system, each measurement changes the wavefunction of the measured system in accordance with the measurement result, and therefore the statistics of each measurement result depend on the results of all the previous measurements. The quantum measurement which does not change the wavefunction of the measured system at all requires full a-priori knowledge of this wavefunction. We show that this impossibility of determining the quantum wavefunction of a single system and the quantum Zeno effect of a single system are equivalent. These effects impose a fundamental limit to precision measurement techniques. We show that in the detection of an external force via the monitoring of a single quantum harmonic oscillator, this limit requires an exchange of at least one quantum of energy between the force and the oscillator. [E5.02] Resonant Dipole-Dipole Collisions of Rydberg Atoms in a Magneto-Optical Trap W. R. Anderson (University of Virginia, Charlottesville, VA 22901) I present a study of resonant energy transfer via a dipole-dipole interaction between alkali atoms in Rydberg states. We have studied such interactions between atoms prepared in a magneto-optical trap (MOT). In binary collisions the atomic density plays no role in the collision dynamics, however, using laser cooling and trapping techniques we have been able to enter a new regime for resonant energy transfer. In this regime the resonance widths are described by a model in which the atoms are ``frozen'' in place during a collision. We also exploit the long interaction times of the cold atoms in a MOT to observe Ramsey interference fringes in resonant energy transfer between rubidium atoms. A manifestation of electromagnetically induced transparency in potassium Rydberg atom collisions is also presented. [E5.03] Bose-Einstein condensation in atomic alkali gases Robert J. Dodd (Department of Physics, Oxford University, United Kingdom) I present a review of the time-independent Gross-Pitaevskii (GP), Bogoliubov, and finite-temperature Hartree-Fock-Bogoliubov (HFB) mean-field theories used to study trapped, Bose-Einstein condensed alkali gases. Numerical solutions of the (zero-temperature) GP equation are presented for attractive (negative scattering length) and repulsive (positive scattering length) interactions. Comparison is made with the Thomas-Fermi and (variational) trial wavefunction appr oximations that are used in the literature to study condensed gases. Numerical calculations of the (zero-temperature) Bogoliubov quasi-particle excitation frequencies are found to be in excellent agreement with the experimental results. The finite-temperature properties of condensed gases are examined using the Popov approximation (of the HFB theory) and a simple two-gas model. Specific, quantitative comparisons are made with experimental results for finite-temperature excitation frequencies. Qualitative comparisons are made between the results of the Popov approximation, two-gas model, and other published models for condensate fraction and thermal density distribution. The time-independent mean-field theories are found to be in excellent agreement with experimental results at relatively low temperatures (high condensate fractions). However, at higher temperatures (and condensate fractions of less than 50%) there are significant discrepancies between experimental data and theoretical calculations. This work was undertaken at the University of Maryland at College Park and was supported in part by the National Science Foundation (PHY-9601261) and the U.S. Office of Naval Research. [E5.04] Rydberg Wave Packets and Half-Cycle Electromagnetic Pulses Chandra S. Raman (Massachusetts Institute of Technology) This dissertation summarizes an examination of the dynamics of atomic Rydberg wave packets with coherent pulses of THz electromagnetic radiation consisting of less than a single cycle of the electric field. The bulk of the energy is contained in just a half-cycle. Previous work ( R.~Jones, D.~You, and P.~Bucksbaum, ``Ionization of Rydberg atoms by subpicosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~70, 1993. had shown how these half-cycle pulses can be used to ionize the highly excited states of an atom, and that a classical view of electronic motion in the atom explains the ionization mechanism. To further probe the boundary between classical trajectories and quantum mechanics, in this work I investigate dynamical combinations of Rydberg states, or Rydberg wave packets, and how they ionize under the influence of a half-cycle electromagnetic pulse. With time-domain techniques I am able to extract the dynamics of the wave packet from the ionization rate, and to observe wave packet motion in both the electronic radial ( C.~Raman, C.~Conover, C.~Sukenik, and P.~Bucksbaum, ``Ionization of Rydberg wavepackets by sub-picosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~76, 1996.and angular ( C.~Raman, T.~Weinacht, and P.~Bucksbaum, ``Stark wavepackets viewed with half cycle pulses.'' Phys. Rev. A), vol.~ 55, No. 6, 1997. coordinates. This is the first time a wavepacket technique has been used to view electron motion everywhere on its trajectory, and not just at the nucleus. This is the principal feature of half-cycle pulse ionization. Semiclassical ideas of ionization in conjunction with quantum descriptions of the wave packet, are capable of reproducing the main trends in the data, and in the absence of a rigorous model I rely on these. Experiments of this nature provide examples of the ongoing effort to use the coherent properties of radiation to control electronic motion in an atom, as well as to probe the boundaries between quantum and classical mechanics. [E5.05] Improved measurement of parity nonconservation in atomic cesium and first measurement of the nuclear anapole moment Chris Wood (JILA and University of Colorado, Boulder) Historically, atomic parity nonconservation (PNC) measurements have bridged the gap between high energy and low energy physics. Our recently completed 0.35% measurement of PNC in cesium(C. S. Wood extit et al., Science) extbf 275, 1759 (1997) has gone a step further and created a bridge between atomic physics and nuclear physics. This measurement represents the best low energy test of electroweak unification and, in addition, we have made a 14% measurement of the parity violating nuclear anapole moment(V.V. Flambaum extit et al., Phys. Lett. B) extbf 146, 367 (1984). Cesium continues to hold a special place for atomic PNC measurements due to the accuracy (1%) with which the necessary atomic structure calculations can be made(S.A. Blundell, J. Sapirstein, and W. R. Johnson, extit Phys. Rev. D) extbf 45, 1602 (1992); V.A. Dzuba, V. V. Flambaum, and O. P. Sushkov, Phys. Lett. A 141, 147 (1989)., and our result has motivated new calculations. The experiment uses a Stark interference technique to measure PNC, and has achieved a factor of seven improvement over our previous result. Two frequency-stabilized diode lasers are used to optically pump an intense cesium beam, while a third is used for detection and a fourth is used to monitor the spin polarization of the atomic beam using stimulated Raman transitions. A dye laser operating at 540nm, phase locked to a finesse 100,000 power buildup cavity, is used to excite the forbidden 6S-7S transition in a region of crossed electric and magnetic fields. These fields serve to define an experimental coordinate system. We have developed 5 different ways to parity transform this coordinate system, which are crucial to our ability to suppress systematic errors. Our signal is the interference of an allowed 6S-7S transition amplitude with the PNC transition amplitude, which causes a tiny (6 ppm) fractional modulation of the 6S-7S excitation rate synchronous with all 5 parity transformations. Previous session | Next session Session E5 - Atomic, Molecular and Optical Physics Thesis Award. INVITED session, Thursday morning, May 28 Mesa Ballroom, Hilton [E5.01] Impossibility of Determining the Quantum Wavefunction of a Single System and Fundamental Limit to External Force Detection Orly Alter (ERATO Quantum Fluctuation Project, Stanford University) Technology has advanced to the point that single quantum systems can now be controlled. Due to these advances, fundamental questions in quantum theory are being faced in laboratories all over the world. The possibility of performing a series of measurements on a single quantum system has renewed interest in the question of the physical reality of the wavefunction: what is the fundamental limit to the determination of the quantum wavefunction of a single system? Recently, Aharonov et. al. suggested that it may be possible to determine the unknown quantum wavefunction of a single system. State-of-the-art precision measurements, which are based on the monitoring of the time evolution of a single physical system, has renewed interest in the question of the quantum Zeno effect of a single system: what is the fundamental limit to the determination of the time evolution of a single system? And to the detection of a classical signal via the monitoring of a single system? Braginsky et. al., Caves et. al. and Yuen suggested independently that there may be no limit to the detection of an external force via the monitoring of a single quantum harmonic oscillator. This dissertation establishes the quantum theoretical limits to the information which can be obtained in the measurement of a single system. We prove that information about the unknown quantum wavefunction of the system is limited to estimates of the expectation values of the measured observables, where the estimate errors satisfy the uncertainty principle. This is due to the reduction process: in a series of measurements of a single system, each measurement changes the wavefunction of the measured system in accordance with the measurement result, and therefore the statistics of each measurement result depend on the results of all the previous measurements. The quantum measurement which does not change the wavefunction of the measured system at all requires full a-priori knowledge of this wavefunction. We show that this impossibility of determining the quantum wavefunction of a single system and the quantum Zeno effect of a single system are equivalent. These effects impose a fundamental limit to precision measurement techniques. We show that in the detection of an external force via the monitoring of a single quantum harmonic oscillator, this limit requires an exchange of at least one quantum of energy between the force and the oscillator. [E5.02] Resonant Dipole-Dipole Collisions of Rydberg Atoms in a Magneto-Optical Trap W. R. Anderson (University of Virginia, Charlottesville, VA 22901) I present a study of resonant energy transfer via a dipole-dipole interaction between alkali atoms in Rydberg states. We have studied such interactions between atoms prepared in a magneto-optical trap (MOT). In binary collisions the atomic density plays no role in the collision dynamics, however, using laser cooling and trapping techniques we have been able to enter a new regime for resonant energy transfer. In this regime the resonance widths are described by a model in which the atoms are ``frozen'' in place during a collision. We also exploit the long interaction times of the cold atoms in a MOT to observe Ramsey interference fringes in resonant energy transfer between rubidium atoms. A manifestation of electromagnetically induced transparency in potassium Rydberg atom collisions is also presented. [E5.03] Bose-Einstein condensation in atomic alkali gases Robert J. Dodd (Department of Physics, Oxford University, United Kingdom) I present a review of the time-independent Gross-Pitaevskii (GP), Bogoliubov, and finite-temperature Hartree-Fock-Bogoliubov (HFB) mean-field theories used to study trapped, Bose-Einstein condensed alkali gases. Numerical solutions of the (zero-temperature) GP equation are presented for attractive (negative scattering length) and repulsive (positive scattering length) interactions. Comparison is made with the Thomas-Fermi and (variational) trial wavefunction appr oximations that are used in the literature to study condensed gases. Numerical calculations of the (zero-temperature) Bogoliubov quasi-particle excitation frequencies are found to be in excellent agreement with the experimental results. The finite-temperature properties of condensed gases are examined using the Popov approximation (of the HFB theory) and a simple two-gas model. Specific, quantitative comparisons are made with experimental results for finite-temperature excitation frequencies. Qualitative comparisons are made between the results of the Popov approximation, two-gas model, and other published models for condensate fraction and thermal density distribution. The time-independent mean-field theories are found to be in excellent agreement with experimental results at relatively low temperatures (high condensate fractions). However, at higher temperatures (and condensate fractions of less than 50%) there are significant discrepancies between experimental data and theoretical calculations. This work was undertaken at the University of Maryland at College Park and was supported in part by the National Science Foundation (PHY-9601261) and the U.S. Office of Naval Research. [E5.04] Rydberg Wave Packets and Half-Cycle Electromagnetic Pulses Chandra S. Raman (Massachusetts Institute of Technology) This dissertation summarizes an examination of the dynamics of atomic Rydberg wave packets with coherent pulses of THz electromagnetic radiation consisting of less than a single cycle of the electric field. The bulk of the energy is contained in just a half-cycle. Previous work ( R.~Jones, D.~You, and P.~Bucksbaum, ``Ionization of Rydberg atoms by subpicosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~70, 1993. had shown how these half-cycle pulses can be used to ionize the highly excited states of an atom, and that a classical view of electronic motion in the atom explains the ionization mechanism. To further probe the boundary between classical trajectories and quantum mechanics, in this work I investigate dynamical combinations of Rydberg states, or Rydberg wave packets, and how they ionize under the influence of a half-cycle electromagnetic pulse. With time-domain techniques I am able to extract the dynamics of the wave packet from the ionization rate, and to observe wave packet motion in both the electronic radial ( C.~Raman, C.~Conover, C.~Sukenik, and P.~Bucksbaum, ``Ionization of Rydberg wavepackets by sub-picosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~76, 1996.and angular ( C.~Raman, T.~Weinacht, and P.~Bucksbaum, ``Stark wavepackets viewed with half cycle pulses.'' Phys. Rev. A), vol.~ 55, No. 6, 1997. coordinates. This is the first time a wavepacket technique has been used to view electron motion everywhere on its trajectory, and not just at the nucleus. This is the principal feature of half-cycle pulse ionization. Semiclassical ideas of ionization in conjunction with quantum descriptions of the wave packet, are capable of reproducing the main trends in the data, and in the absence of a rigorous model I rely on these. Experiments of this nature provide examples of the ongoing effort to use the coherent properties of radiation to control electronic motion in an atom, as well as to probe the boundaries between quantum and classical mechanics. [E5.05] Improved measurement of parity nonconservation in atomic cesium and first measurement of the nuclear anapole moment Chris Wood (JILA and University of Colorado, Boulder) Historically, atomic parity nonconservation (PNC) measurements have bridged the gap between high energy and low energy physics. Our recently completed 0.35% measurement of PNC in cesium(C. S. Wood extit et al., Science) extbf 275, 1759 (1997) has gone a step further and created a bridge between atomic physics and nuclear physics. This measurement represents the best low energy test of electroweak unification and, in addition, we have made a 14% measurement of the parity violating nuclear anapole moment(V.V. Flambaum extit et al., Phys. Lett. B) extbf 146, 367 (1984). Cesium continues to hold a special place for atomic PNC measurements due to the accuracy (1%) with which the necessary atomic structure calculations can be made(S.A. Blundell, J. Sapirstein, and W. R. Johnson, extit Phys. Rev. D) extbf 45, 1602 (1992); V.A. Dzuba, V. V. Flambaum, and O. P. Sushkov, Phys. Lett. A 141, 147 (1989)., and our result has motivated new calculations. The experiment uses a Stark interference technique to measure PNC, and has achieved a factor of seven improvement over our previous result. Two frequency-stabilized diode lasers are used to optically pump an intense cesium beam, while a third is used for detection and a fourth is used to monitor the spin polarization of the atomic beam using stimulated Raman transitions. A dye laser operating at 540nm, phase locked to a finesse 100,000 power buildup cavity, is used to excite the forbidden 6S-7S transition in a region of crossed electric and magnetic fields. These fields serve to define an experimental coordinate system. We have developed 5 different ways to parity transform this coordinate system, which are crucial to our ability to suppress systematic errors. Our signal is the interference of an allowed 6S-7S transition amplitude with the PNC transition amplitude, which causes a tiny (6 ppm) fractional modulation of the 6S-7S excitation rate synchronous with all 5 parity transformations. Previous session | Next session Session E5 - Atomic, Molecular and Optical Physics Thesis Award. INVITED session, Thursday morning, May 28 Mesa Ballroom, Hilton [E5.01] Impossibility of Determining the Quantum Wavefunction of a Single System and Fundamental Limit to External Force Detection Orly Alter (ERATO Quantum Fluctuation Project, Stanford University) Technology has advanced to the point that single quantum systems can now be controlled. Due to these advances, fundamental questions in quantum theory are being faced in laboratories all over the world. The possibility of performing a series of measurements on a single quantum system has renewed interest in the question of the physical reality of the wavefunction: what is the fundamental limit to the determination of the quantum wavefunction of a single system? Recently, Aharonov et. al. suggested that it may be possible to determine the unknown quantum wavefunction of a single system. State-of-the-art precision measurements, which are based on the monitoring of the time evolution of a single physical system, has renewed interest in the question of the quantum Zeno effect of a single system: what is the fundamental limit to the determination of the time evolution of a single system? And to the detection of a classical signal via the monitoring of a single system? Braginsky et. al., Caves et. al. and Yuen suggested independently that there may be no limit to the detection of an external force via the monitoring of a single quantum harmonic oscillator. This dissertation establishes the quantum theoretical limits to the information which can be obtained in the measurement of a single system. We prove that information about the unknown quantum wavefunction of the system is limited to estimates of the expectation values of the measured observables, where the estimate errors satisfy the uncertainty principle. This is due to the reduction process: in a series of measurements of a single system, each measurement changes the wavefunction of the measured system in accordance with the measurement result, and therefore the statistics of each measurement result depend on the results of all the previous measurements. The quantum measurement which does not change the wavefunction of the measured system at all requires full a-priori knowledge of this wavefunction. We show that this impossibility of determining the quantum wavefunction of a single system and the quantum Zeno effect of a single system are equivalent. These effects impose a fundamental limit to precision measurement techniques. We show that in the detection of an external force via the monitoring of a single quantum harmonic oscillator, this limit requires an exchange of at least one quantum of energy between the force and the oscillator. [E5.02] Resonant Dipole-Dipole Collisions of Rydberg Atoms in a Magneto-Optical Trap W. R. Anderson (University of Virginia, Charlottesville, VA 22901) I present a study of resonant energy transfer via a dipole-dipole interaction between alkali atoms in Rydberg states. We have studied such interactions between atoms prepared in a magneto-optical trap (MOT). In binary collisions the atomic density plays no role in the collision dynamics, however, using laser cooling and trapping techniques we have been able to enter a new regime for resonant energy transfer. In this regime the resonance widths are described by a model in which the atoms are ``frozen'' in place during a collision. We also exploit the long interaction times of the cold atoms in a MOT to observe Ramsey interference fringes in resonant energy transfer between rubidium atoms. A manifestation of electromagnetically induced transparency in potassium Rydberg atom collisions is also presented. [E5.03] Bose-Einstein condensation in atomic alkali gases Robert J. Dodd (Department of Physics, Oxford University, United Kingdom) I present a review of the time-independent Gross-Pitaevskii (GP), Bogoliubov, and finite-temperature Hartree-Fock-Bogoliubov (HFB) mean-field theories used to study trapped, Bose-Einstein condensed alkali gases. Numerical solutions of the (zero-temperature) GP equation are presented for attractive (negative scattering length) and repulsive (positive scattering length) interactions. Comparison is made with the Thomas-Fermi and (variational) trial wavefunction appr oximations that are used in the literature to study condensed gases. Numerical calculations of the (zero-temperature) Bogoliubov quasi-particle excitation frequencies are found to be in excellent agreement with the experimental results. The finite-temperature properties of condensed gases are examined using the Popov approximation (of the HFB theory) and a simple two-gas model. Specific, quantitative comparisons are made with experimental results for finite-temperature excitation frequencies. Qualitative comparisons are made between the results of the Popov approximation, two-gas model, and other published models for condensate fraction and thermal density distribution. The time-independent mean-field theories are found to be in excellent agreement with experimental results at relatively low temperatures (high condensate fractions). However, at higher temperatures (and condensate fractions of less than 50%) there are significant discrepancies between experimental data and theoretical calculations. This work was undertaken at the University of Maryland at College Park and was supported in part by the National Science Foundation (PHY-9601261) and the U.S. Office of Naval Research. [E5.04] Rydberg Wave Packets and Half-Cycle Electromagnetic Pulses Chandra S. Raman (Massachusetts Institute of Technology) This dissertation summarizes an examination of the dynamics of atomic Rydberg wave packets with coherent pulses of THz electromagnetic radiation consisting of less than a single cycle of the electric field. The bulk of the energy is contained in just a half-cycle. Previous work ( R.~Jones, D.~You, and P.~Bucksbaum, ``Ionization of Rydberg atoms by subpicosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~70, 1993. had shown how these half-cycle pulses can be used to ionize the highly excited states of an atom, and that a classical view of electronic motion in the atom explains the ionization mechanism. To further probe the boundary between classical trajectories and quantum mechanics, in this work I investigate dynamical combinations of Rydberg states, or Rydberg wave packets, and how they ionize under the influence of a half-cycle electromagnetic pulse. With time-domain techniques I am able to extract the dynamics of the wave packet from the ionization rate, and to observe wave packet motion in both the electronic radial ( C.~Raman, C.~Conover, C.~Sukenik, and P.~Bucksbaum, ``Ionization of Rydberg wavepackets by sub-picosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~76, 1996.and angular ( C.~Raman, T.~Weinacht, and P.~Bucksbaum, ``Stark wavepackets viewed with half cycle pulses.'' Phys. Rev. A), vol.~ 55, No. 6, 1997. coordinates. This is the first time a wavepacket technique has been used to view electron motion everywhere on its trajectory, and not just at the nucleus. This is the principal feature of half-cycle pulse ionization. Semiclassical ideas of ionization in conjunction with quantum descriptions of the wave packet, are capable of reproducing the main trends in the data, and in the absence of a rigorous model I rely on these. Experiments of this nature provide examples of the ongoing effort to use the coherent properties of radiation to control electronic motion in an atom, as well as to probe the boundaries between quantum and classical mechanics. [E5.05] Improved measurement of parity nonconservation in atomic cesium and first measurement of the nuclear anapole moment Chris Wood (JILA and University of Colorado, Boulder) Historically, atomic parity nonconservation (PNC) measurements have bridged the gap between high energy and low energy physics. Our recently completed 0.35% measurement of PNC in cesium(C. S. Wood extit et al., Science) extbf 275, 1759 (1997) has gone a step further and created a bridge between atomic physics and nuclear physics. This measurement represents the best low energy test of electroweak unification and, in addition, we have made a 14% measurement of the parity violating nuclear anapole moment(V.V. Flambaum extit et al., Phys. Lett. B) extbf 146, 367 (1984). Cesium continues to hold a special place for atomic PNC measurements due to the accuracy (1%) with which the necessary atomic structure calculations can be made(S.A. Blundell, J. Sapirstein, and W. R. Johnson, extit Phys. Rev. D) extbf 45, 1602 (1992); V.A. Dzuba, V. V. Flambaum, and O. P. Sushkov, Phys. Lett. A 141, 147 (1989)., and our result has motivated new calculations. The experiment uses a Stark interference technique to measure PNC, and has achieved a factor of seven improvement over our previous result. Two frequency-stabilized diode lasers are used to optically pump an intense cesium beam, while a third is used for detection and a fourth is used to monitor the spin polarization of the atomic beam using stimulated Raman transitions. A dye laser operating at 540nm, phase locked to a finesse 100,000 power buildup cavity, is used to excite the forbidden 6S-7S transition in a region of crossed electric and magnetic fields. These fields serve to define an experimental coordinate system. We have developed 5 different ways to parity transform this coordinate system, which are crucial to our ability to suppress systematic errors. Our signal is the interference of an allowed 6S-7S transition amplitude with the PNC transition amplitude, which causes a tiny (6 ppm) fractional modulation of the 6S-7S excitation rate synchronous with all 5 parity transformations. Previous session | Next session Session E5 - Atomic, Molecular and Optical Physics Thesis Award. INVITED session, Thursday morning, May 28 Mesa Ballroom, Hilton [E5.01] Impossibility of Determining the Quantum Wavefunction of a Single System and Fundamental Limit to External Force Detection Orly Alter (ERATO Quantum Fluctuation Project, Stanford University) Technology has advanced to the point that single quantum systems can now be controlled. Due to these advances, fundamental questions in quantum theory are being faced in laboratories all over the world. The possibility of performing a series of measurements on a single quantum system has renewed interest in the question of the physical reality of the wavefunction: what is the fundamental limit to the determination of the quantum wavefunction of a single system? Recently, Aharonov et. al. suggested that it may be possible to determine the unknown quantum wavefunction of a single system. State-of-the-art precision measurements, which are based on the monitoring of the time evolution of a single physical system, has renewed interest in the question of the quantum Zeno effect of a single system: what is the fundamental limit to the determination of the time evolution of a single system? And to the detection of a classical signal via the monitoring of a single system? Braginsky et. al., Caves et. al. and Yuen suggested independently that there may be no limit to the detection of an external force via the monitoring of a single quantum harmonic oscillator. This dissertation establishes the quantum theoretical limits to the information which can be obtained in the measurement of a single system. We prove that information about the unknown quantum wavefunction of the system is limited to estimates of the expectation values of the measured observables, where the estimate errors satisfy the uncertainty principle. This is due to the reduction process: in a series of measurements of a single system, each measurement changes the wavefunction of the measured system in accordance with the measurement result, and therefore the statistics of each measurement result depend on the results of all the previous measurements. The quantum measurement which does not change the wavefunction of the measured system at all requires full a-priori knowledge of this wavefunction. We show that this impossibility of determining the quantum wavefunction of a single system and the quantum Zeno effect of a single system are equivalent. These effects impose a fundamental limit to precision measurement techniques. We show that in the detection of an external force via the monitoring of a single quantum harmonic oscillator, this limit requires an exchange of at least one quantum of energy between the force and the oscillator. [E5.02] Resonant Dipole-Dipole Collisions of Rydberg Atoms in a Magneto-Optical Trap W. R. Anderson (University of Virginia, Charlottesville, VA 22901) I present a study of resonant energy transfer via a dipole-dipole interaction between alkali atoms in Rydberg states. We have studied such interactions between atoms prepared in a magneto-optical trap (MOT). In binary collisions the atomic density plays no role in the collision dynamics, however, using laser cooling and trapping techniques we have been able to enter a new regime for resonant energy transfer. In this regime the resonance widths are described by a model in which the atoms are ``frozen'' in place during a collision. We also exploit the long interaction times of the cold atoms in a MOT to observe Ramsey interference fringes in resonant energy transfer between rubidium atoms. A manifestation of electromagnetically induced transparency in potassium Rydberg atom collisions is also presented. [E5.03] Bose-Einstein condensation in atomic alkali gases Robert J. Dodd (Department of Physics, Oxford University, United Kingdom) I present a review of the time-independent Gross-Pitaevskii (GP), Bogoliubov, and finite-temperature Hartree-Fock-Bogoliubov (HFB) mean-field theories used to study trapped, Bose-Einstein condensed alkali gases. Numerical solutions of the (zero-temperature) GP equation are presented for attractive (negative scattering length) and repulsive (positive scattering length) interactions. Comparison is made with the Thomas-Fermi and (variational) trial wavefunction appr oximations that are used in the literature to study condensed gases. Numerical calculations of the (zero-temperature) Bogoliubov quasi-particle excitation frequencies are found to be in excellent agreement with the experimental results. The finite-temperature properties of condensed gases are examined using the Popov approximation (of the HFB theory) and a simple two-gas model. Specific, quantitative comparisons are made with experimental results for finite-temperature excitation frequencies. Qualitative comparisons are made between the results of the Popov approximation, two-gas model, and other published models for condensate fraction and thermal density distribution. The time-independent mean-field theories are found to be in excellent agreement with experimental results at relatively low temperatures (high condensate fractions). However, at higher temperatures (and condensate fractions of less than 50%) there are significant discrepancies between experimental data and theoretical calculations. This work was undertaken at the University of Maryland at College Park and was supported in part by the National Science Foundation (PHY-9601261) and the U.S. Office of Naval Research. [E5.04] Rydberg Wave Packets and Half-Cycle Electromagnetic Pulses Chandra S. Raman (Massachusetts Institute of Technology) This dissertation summarizes an examination of the dynamics of atomic Rydberg wave packets with coherent pulses of THz electromagnetic radiation consisting of less than a single cycle of the electric field. The bulk of the energy is contained in just a half-cycle. Previous work ( R.~Jones, D.~You, and P.~Bucksbaum, ``Ionization of Rydberg atoms by subpicosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~70, 1993. had shown how these half-cycle pulses can be used to ionize the highly excited states of an atom, and that a classical view of electronic motion in the atom explains the ionization mechanism. To further probe the boundary between classical trajectories and quantum mechanics, in this work I investigate dynamical combinations of Rydberg states, or Rydberg wave packets, and how they ionize under the influence of a half-cycle electromagnetic pulse. With time-domain techniques I am able to extract the dynamics of the wave packet from the ionization rate, and to observe wave packet motion in both the electronic radial ( C.~Raman, C.~Conover, C.~Sukenik, and P.~Bucksbaum, ``Ionization of Rydberg wavepackets by sub-picosecond half-cycle electromagnetic pulses,'' Phys. Rev. Lett.), vol.~76, 1996.and angular ( C.~Raman, T.~Weinacht, and P.~Bucksbaum, ``Stark wavepackets viewed with half cycle pulses.'' Phys. Rev. A), vol.~ 55, No. 6, 1997. coordinates. This is the first time a wavepacket technique has been used to view electron motion everywhere on its trajectory, and not just at the nucleus. This is the principal feature of half-cycle pulse ionization. Semiclassical ideas of ionization in conjunction with quantum descriptions of the wave packet, are capable of reproducing the main trends in the data, and in the absence of a rigorous model I rely on these. Experiments of this nature provide examples of the ongoing effort to use the coherent properties of radiation to control electronic motion in an atom, as well as to probe the boundaries between quantum and classical mechanics. [E5.05] Improved measurement of parity nonconservation in atomic cesium and first measurement of the nuclear anapole moment Chris Wood (JILA and University of Colorado, Boulder) Historically, atomic parity nonconservation (PNC) measurements have bridged the gap between high energy and low energy physics. Our recently completed 0.35% measurement of PNC in cesium(C. S. Wood extit et al., Science) extbf 275, 1759 (1997) has gone a step further and created a bridge between atomic physics and nuclear physics. This measurement represents the best low energy test of electroweak unification and, in addition, we have made a 14% measurement of the parity violating nuclear anapole moment(V.V. Flambaum extit et al., Phys. Lett. B) extbf 146, 367 (1984). Cesium continues to hold a special place for atomic PNC measurements due to the accuracy (1%) with which the necessary atomic structure calculations can be made(S.A. Blundell, J. Sapirstein, and W. R. Johnson, extit Phys. Rev. D) extbf 45, 1602 (1992); V.A. Dzuba, V. V. Flambaum, and O. P. Sushkov, Phys. Lett. A 141, 147 (1989)., and our result has motivated new calculations. The experiment uses a Stark interference technique to measure PNC, and has achieved a factor of seven improvement over our previous result. Two frequency-stabilized diode lasers are used to optically pump an intense cesium beam, while a third is used for detection and a fourth is used to monitor the spin polarization of the atomic beam using stimulated Raman transitions. A dye laser operating at 540nm, phase locked to a finesse 100,000 power buildup cavity, is used to excite the forbidden 6S-7S transition in a region of crossed electric and magnetic fields. These fields serve to define an experimental coordinate system. We have developed 5 different ways to parity transform this coordinate system, which are crucial to our ability to suppress systematic errors. Our signal is the interference of an allowed 6S-7S transition amplitude with the PNC transition amplitude, which causes a tiny (6 ppm) fractional modulation of the 6S-7S excitation rate synchronous with all 5 parity transformations.