Ten years ago, the new era of time crystals began. Time crystals are systems that behave in the t... more Ten years ago, the new era of time crystals began. Time crystals are systems that behave in the time dimension like ordinary space crystals do in space dimensions. We present a brief history of a decade of research on time crystals, describe current research directions, indicate challenges, and discuss some future perspectives for condensed matter physics in the time domain.
We report the investigation of the wave-mixing and amplification process with two multiple-cycle ... more We report the investigation of the wave-mixing and amplification process with two multiple-cycle pulses with incommensurate frequencies (at 1400 nm and 800 nm). With a non-collinear configuration of the two beams, a different extreme ultraviolet mixing field can be created at low intensity of the 800 nm field. When a very high intensity 800 nm pulse is applied we are able to amplify the coherent extreme ultraviolet radiation in the photon energy range around 80 eV.
We report the generation of extreme ultraviolet radiation with high photon flux (1010–1012 photon... more We report the generation of extreme ultraviolet radiation with high photon flux (1010–1012 photon/cm2 s), high spatial coherence (up to 0.95), and good spatial beam profile by high-order harmonic generation in various noble gases (argon, neon, and helium) in a gas cell. The photon flux was determined using an extreme ultraviolet spectrometer equipped with a charge-coupled device camera and the spatial coherence was determined from Young double-slit interference fringes. The high-order harmonic emission is confined to just a few orders because of the small phase mismatch in the cut-off region that allows macroscopic phase matching to be satisfied for just a few harmonics in this region. The efficiency and spatial beam profile are studied as a function of gas pressure and geometrical configuration.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005
Storage of light pulses in Rb vapour with bright Zeeman coherences and the associated enhanced ab... more Storage of light pulses in Rb vapour with bright Zeeman coherences and the associated enhanced absorption and steep negative dispersion is reported. Our experimental observations are qualitatively similar to the well-known proof-of-principle demonstration of light storage (D F Phillips et al 2001 Phys. Rev. Lett. 86 783), but obtained under conditions where electromagnetically induced transparency (EIT) does not exist and
A lifetimes technique that is readily applicable to neutral and singly ionised atoms of a wide ra... more A lifetimes technique that is readily applicable to neutral and singly ionised atoms of a wide range of elements, including the highly refractory elements, is reviewed. With this technique an atomic vapour of the element under study is generated by cathodic sputtering in a low pressure rare-gas discharge and fluorescence decay signals emitted by the vapour following pulsed laser excitation are recorded directly in a fast transient digitiser. Theoretical expressions are presented for the form of the time-resolved fluor~scence signal appropriate to the collisional environment of a rare-gas sputtering discharge. A summary is given of the atomic systems studied to date using this technique, and some new results for Sm and Ba are compared with recently reported results for these elements.
Room temperature atomic ensembles in a spin-protected environment are useful systems both for qua... more Room temperature atomic ensembles in a spin-protected environment are useful systems both for quantum information science and metrology. Here we utilize a setup consisting of two atomic ensembles as a memory for quantum information initially encoded in the polarization state of two entangled light modes. We also use the ensembles as a radio frequency entanglement-assisted magnetometer with projection noise limited sensitivity below femtoTesla/ √ Hz. The performance of the quantum memory as well as the magnetometer was improved by spin-squeezed or entangled atomic states generated by quantum non demolition measurements. Finally, we present preliminary results of long lived entangled atomic states generated by dissipation. With the method presented, one should be able to generate an entangled steady state.
Room temperature atomic ensembles in a spin-protected environment are useful systems both for qua... more Room temperature atomic ensembles in a spin-protected environment are useful systems both for quantum information science and metrology. Here we utilize a setup consisting of two atomic ensembles as a memory for quantum information initially encoded in the polarization state of two entangled light modes. We also use the ensembles as a radio frequency entanglement-assisted magnetometer with projection noise limited sensitivity below femtoTesla/ √ Hz. The performance of the quantum memory as well as the magnetometer was improved by spin-squeezed or entangled atomic states generated by quantum non demolition measurements. Finally, we present preliminary results of long lived entangled atomic states generated by dissipation. With the method presented, one should be able to generate an entangled steady state.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
The nonlinear properties of an undoped GaN epitaxial layer in the spectral region of the yellow b... more The nonlinear properties of an undoped GaN epitaxial layer in the spectral region of the yellow band have been investigated using two-and three-pulse two-colour photon echo measurements. The optical nonlinearity induced by three sequential femtosecond pulses is studied on a short timescale (<500 fs) where free induction decay and photon echoes are the main contributions to the observed signal and on a long timescale (up to 20 ps) in the case of a population grating. Variation of the wavelength of the femtosecond pulses and the use of spectrally resolved measurements allows us to study the origin of the yellow band and the phase and energy relaxation properties of this band. The results suggest that the emission of light in the yellow band arises from recombination between shallow donors and deep acceptors and that the trapping time of carriers into defect levels is very short (<1 ps).
Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1988
A technique based on the detection of nonlinear level-crossing resonances in finite magnetic fiel... more A technique based on the detection of nonlinear level-crossing resonances in finite magnetic fields has been extended to the study of high-lying electronic levels excited by stepwise excitation with two cw dye lasers. The method has been applied to the determination of IA/gj[ values for four highly excited even-parity levels and two odd-parity levels in yttrium I. Using recently determined values of the magnetic hyperfine interaction constant A, Land6 g j-factors have been deduced for these levels with an accuracy of about 1%. The results show significant differences from previous determinations.
Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1986
Absorption line narrowing techniques have been used to make original measurements of hyperfine st... more Absorption line narrowing techniques have been used to make original measurements of hyperfine structure in twelve highly excited levels of atomic yttrium. The yttrium vapour, produced by cathodic sputtering in a low pressure, rare-gas discharge, was excited by stepwise excitation with two narrow-band cw lasers. Doppler-free signals have been recorded using both fluorescence and optogalvanic detection. Resonances as narrow as 6 MHz FWHM have been observed in the discharge.
ABSTRACT Both long-lived coherences and coherent population oscillations result in dramatic enhan... more ABSTRACT Both long-lived coherences and coherent population oscillations result in dramatic enhancement of a Kerr nonlinearity in atomic media at very low intensity of resonant light. We demonstrate the possibility of separating the contributions from these effects under certain experimental conditions. We report a study of the nonlinear optical properties of atomic media under a variety of experimental conditions at low light intensity, paying particular attention to self-focussing, diffraction and quasi-degenerate wave mixing.
... example, in the flame atomic absorption studies of Willis (1971), use of our value f2676 = 0.... more ... example, in the flame atomic absorption studies of Willis (1971), use of our value f2676 = 0.176 * 0.003 in place of the result of Lawrence et a1 (f2676 = 0.125 ... Acta 14 349-59 Ashenfelter R C 1967 PhD Thesis California Institute of Technology Bates D and Damgaard A 1949 Phil ...
Both long-lived coherences and coherent population oscillations result in dramatic enhancement of... more Both long-lived coherences and coherent population oscillations result in dramatic enhancement of a Kerr nonlinearity in atomic media at very low intensity of resonant light. We demonstrate the possibility of separating the contributions from these effects under certain experimental conditions. We report a study of the nonlinear optical properties of atomic media under a variety of experimental conditions at low light intensity, paying particular attention to self-focussing, diffraction and quasi-degenerate wave mixing.
The 22nd International Conference on Atomic Physics (ICAP 2010) was held from 25 to 30 July, 2010... more The 22nd International Conference on Atomic Physics (ICAP 2010) was held from 25 to 30 July, 2010 in Cairns, Tropical North Queensland, Australia. This conference followed on from the series of highly successful biennial ICAP conferences held in Storrs, Innsbruck, Rio, Cambridge MA, Florence, Windsor, Amsterdam, Boulder, Munich, Ann Arbor, Paris, Tokyo, Seattle, Göteborg, Cambridge MA, Riga, Berkeley, Heidelberg, Boulder, Oxford and New York. ICAP 2010 was attended by 630 participants from 37 countries. The conference presented an outstanding program of papers covering the most recent advances in atomic physics, including atomic tests of fundamental physics and basic symmetries; precision measurements, including atomic clocks, atom interferometers and fundamental constants; ultracold gases and Bose-Einstein condensates; ultracold Fermi gases; ultracold molecules; quantum simulators with atoms and ions; few-body systems; ultrafast phenomena and free electron lasers; quantum informati...
We report an enhancement, by a factor of two, of the cut-off energy of high-harmonic radiation ge... more We report an enhancement, by a factor of two, of the cut-off energy of high-harmonic radiation generated in a semi-infinitive gas cell when laser pulses with energy 2 mJ and wavelength 1300 nm are applied, compared with 800 nm pulses. Water window radiation (~ 4.4 nm) is generated by using helium gas.
Ten years ago, the new era of time crystals began. Time crystals are systems that behave in the t... more Ten years ago, the new era of time crystals began. Time crystals are systems that behave in the time dimension like ordinary space crystals do in space dimensions. We present a brief history of a decade of research on time crystals, describe current research directions, indicate challenges, and discuss some future perspectives for condensed matter physics in the time domain.
We report the investigation of the wave-mixing and amplification process with two multiple-cycle ... more We report the investigation of the wave-mixing and amplification process with two multiple-cycle pulses with incommensurate frequencies (at 1400 nm and 800 nm). With a non-collinear configuration of the two beams, a different extreme ultraviolet mixing field can be created at low intensity of the 800 nm field. When a very high intensity 800 nm pulse is applied we are able to amplify the coherent extreme ultraviolet radiation in the photon energy range around 80 eV.
We report the generation of extreme ultraviolet radiation with high photon flux (1010–1012 photon... more We report the generation of extreme ultraviolet radiation with high photon flux (1010–1012 photon/cm2 s), high spatial coherence (up to 0.95), and good spatial beam profile by high-order harmonic generation in various noble gases (argon, neon, and helium) in a gas cell. The photon flux was determined using an extreme ultraviolet spectrometer equipped with a charge-coupled device camera and the spatial coherence was determined from Young double-slit interference fringes. The high-order harmonic emission is confined to just a few orders because of the small phase mismatch in the cut-off region that allows macroscopic phase matching to be satisfied for just a few harmonics in this region. The efficiency and spatial beam profile are studied as a function of gas pressure and geometrical configuration.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005
Storage of light pulses in Rb vapour with bright Zeeman coherences and the associated enhanced ab... more Storage of light pulses in Rb vapour with bright Zeeman coherences and the associated enhanced absorption and steep negative dispersion is reported. Our experimental observations are qualitatively similar to the well-known proof-of-principle demonstration of light storage (D F Phillips et al 2001 Phys. Rev. Lett. 86 783), but obtained under conditions where electromagnetically induced transparency (EIT) does not exist and
A lifetimes technique that is readily applicable to neutral and singly ionised atoms of a wide ra... more A lifetimes technique that is readily applicable to neutral and singly ionised atoms of a wide range of elements, including the highly refractory elements, is reviewed. With this technique an atomic vapour of the element under study is generated by cathodic sputtering in a low pressure rare-gas discharge and fluorescence decay signals emitted by the vapour following pulsed laser excitation are recorded directly in a fast transient digitiser. Theoretical expressions are presented for the form of the time-resolved fluor~scence signal appropriate to the collisional environment of a rare-gas sputtering discharge. A summary is given of the atomic systems studied to date using this technique, and some new results for Sm and Ba are compared with recently reported results for these elements.
Room temperature atomic ensembles in a spin-protected environment are useful systems both for qua... more Room temperature atomic ensembles in a spin-protected environment are useful systems both for quantum information science and metrology. Here we utilize a setup consisting of two atomic ensembles as a memory for quantum information initially encoded in the polarization state of two entangled light modes. We also use the ensembles as a radio frequency entanglement-assisted magnetometer with projection noise limited sensitivity below femtoTesla/ √ Hz. The performance of the quantum memory as well as the magnetometer was improved by spin-squeezed or entangled atomic states generated by quantum non demolition measurements. Finally, we present preliminary results of long lived entangled atomic states generated by dissipation. With the method presented, one should be able to generate an entangled steady state.
Room temperature atomic ensembles in a spin-protected environment are useful systems both for qua... more Room temperature atomic ensembles in a spin-protected environment are useful systems both for quantum information science and metrology. Here we utilize a setup consisting of two atomic ensembles as a memory for quantum information initially encoded in the polarization state of two entangled light modes. We also use the ensembles as a radio frequency entanglement-assisted magnetometer with projection noise limited sensitivity below femtoTesla/ √ Hz. The performance of the quantum memory as well as the magnetometer was improved by spin-squeezed or entangled atomic states generated by quantum non demolition measurements. Finally, we present preliminary results of long lived entangled atomic states generated by dissipation. With the method presented, one should be able to generate an entangled steady state.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
The nonlinear properties of an undoped GaN epitaxial layer in the spectral region of the yellow b... more The nonlinear properties of an undoped GaN epitaxial layer in the spectral region of the yellow band have been investigated using two-and three-pulse two-colour photon echo measurements. The optical nonlinearity induced by three sequential femtosecond pulses is studied on a short timescale (<500 fs) where free induction decay and photon echoes are the main contributions to the observed signal and on a long timescale (up to 20 ps) in the case of a population grating. Variation of the wavelength of the femtosecond pulses and the use of spectrally resolved measurements allows us to study the origin of the yellow band and the phase and energy relaxation properties of this band. The results suggest that the emission of light in the yellow band arises from recombination between shallow donors and deep acceptors and that the trapping time of carriers into defect levels is very short (<1 ps).
Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1988
A technique based on the detection of nonlinear level-crossing resonances in finite magnetic fiel... more A technique based on the detection of nonlinear level-crossing resonances in finite magnetic fields has been extended to the study of high-lying electronic levels excited by stepwise excitation with two cw dye lasers. The method has been applied to the determination of IA/gj[ values for four highly excited even-parity levels and two odd-parity levels in yttrium I. Using recently determined values of the magnetic hyperfine interaction constant A, Land6 g j-factors have been deduced for these levels with an accuracy of about 1%. The results show significant differences from previous determinations.
Zeitschrift f�r Physik D Atoms, Molecules and Clusters, 1986
Absorption line narrowing techniques have been used to make original measurements of hyperfine st... more Absorption line narrowing techniques have been used to make original measurements of hyperfine structure in twelve highly excited levels of atomic yttrium. The yttrium vapour, produced by cathodic sputtering in a low pressure, rare-gas discharge, was excited by stepwise excitation with two narrow-band cw lasers. Doppler-free signals have been recorded using both fluorescence and optogalvanic detection. Resonances as narrow as 6 MHz FWHM have been observed in the discharge.
ABSTRACT Both long-lived coherences and coherent population oscillations result in dramatic enhan... more ABSTRACT Both long-lived coherences and coherent population oscillations result in dramatic enhancement of a Kerr nonlinearity in atomic media at very low intensity of resonant light. We demonstrate the possibility of separating the contributions from these effects under certain experimental conditions. We report a study of the nonlinear optical properties of atomic media under a variety of experimental conditions at low light intensity, paying particular attention to self-focussing, diffraction and quasi-degenerate wave mixing.
... example, in the flame atomic absorption studies of Willis (1971), use of our value f2676 = 0.... more ... example, in the flame atomic absorption studies of Willis (1971), use of our value f2676 = 0.176 * 0.003 in place of the result of Lawrence et a1 (f2676 = 0.125 ... Acta 14 349-59 Ashenfelter R C 1967 PhD Thesis California Institute of Technology Bates D and Damgaard A 1949 Phil ...
Both long-lived coherences and coherent population oscillations result in dramatic enhancement of... more Both long-lived coherences and coherent population oscillations result in dramatic enhancement of a Kerr nonlinearity in atomic media at very low intensity of resonant light. We demonstrate the possibility of separating the contributions from these effects under certain experimental conditions. We report a study of the nonlinear optical properties of atomic media under a variety of experimental conditions at low light intensity, paying particular attention to self-focussing, diffraction and quasi-degenerate wave mixing.
The 22nd International Conference on Atomic Physics (ICAP 2010) was held from 25 to 30 July, 2010... more The 22nd International Conference on Atomic Physics (ICAP 2010) was held from 25 to 30 July, 2010 in Cairns, Tropical North Queensland, Australia. This conference followed on from the series of highly successful biennial ICAP conferences held in Storrs, Innsbruck, Rio, Cambridge MA, Florence, Windsor, Amsterdam, Boulder, Munich, Ann Arbor, Paris, Tokyo, Seattle, Göteborg, Cambridge MA, Riga, Berkeley, Heidelberg, Boulder, Oxford and New York. ICAP 2010 was attended by 630 participants from 37 countries. The conference presented an outstanding program of papers covering the most recent advances in atomic physics, including atomic tests of fundamental physics and basic symmetries; precision measurements, including atomic clocks, atom interferometers and fundamental constants; ultracold gases and Bose-Einstein condensates; ultracold Fermi gases; ultracold molecules; quantum simulators with atoms and ions; few-body systems; ultrafast phenomena and free electron lasers; quantum informati...
We report an enhancement, by a factor of two, of the cut-off energy of high-harmonic radiation ge... more We report an enhancement, by a factor of two, of the cut-off energy of high-harmonic radiation generated in a semi-infinitive gas cell when laser pulses with energy 2 mJ and wavelength 1300 nm are applied, compared with 800 nm pulses. Water window radiation (~ 4.4 nm) is generated by using helium gas.
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Papers by P. Hannaford