We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable ... more We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distribution function of the two-point phase correlation. Comparison to a stochastic model allows to measure the coupling strength and temperature and hence a full characterization of the system.
We propose a novel approach to all-optical frequency standard design, based on a counterintuitive... more We propose a novel approach to all-optical frequency standard design, based on a counterintuitive combination of the coherent population trapping effect and signal discrimination at the maximum of absorption for the probe radiation. The short-term stability of such a standard can achieve the level of 10 −14 / √ τ . The physics beyond this approach is dark resonance splitting caused by interaction of the nuclear magnetic moment with the external magnetic field. PACS numbers: 06.30.Ft, 42.50.Gy, 32.80.Bx The unit of time in the Système International (the second) is defined via the period of the transition between the hyperfine (HF) components of the ground state of the 133 Cs atom (in the limit of vanishing external perturbations). Secondary standards may use other elements (alkali metals, hydrogen). Operation of a frequency standard is provided by locking a microwave signal produced by a quartz crystal oscillator to a resonance on the transition between the working levels [1], i. e. the Zeeman components of the HF structure with zero projection of the total angular momentum. Such a choice of the working levels is dictated by the absence of the linear Zeeman shift. The resonance can be excited by direct microwave transition or by two-photon Raman transition. The latter option provides the basis for all-optical frequency standards where the setup includes no microwave cavities, but electro-optical modulation of the laser beam or direct modulation of the diode laser current are used instead If the interaction time of an atom with the laser field exceeds few optical pumping cycles then the coherent population trapping (CPT) sets in, giving rise to the socalled dark resonance [9, 10]. The physical reason for the CPT is optical pumping of atoms into a coherent superposition of the two ground state sublevels, which is immune to excitation by the frequency-split laser radiation. The CPT leads to decrease of absorption of the laser light. However, if the Raman detuning (the difference between the frequency splitting of the two-component laser radiation and the transition frequency between the two ground state sublevels) exceeds the dark resonance width (what can be as small as few dozens Hz [6, 11]), the CPT atomic state is destroyed, and usual value of the laser radiation absorption is restored.
We measure the two-point density correlation function of freely expanding quasicondensates in the... more We measure the two-point density correlation function of freely expanding quasicondensates in the weakly interacting quasi-one-dimensional (1D) regime. While initially suppressed in the trap, density fluctuations emerge gradually during expansion as a result of initial phase fluctuations present in the trapped quasicondensate. Asymptotically, they are governed by the thermal coherence length of the system. Our measurements take place in an intermediate regime where density correlations are related to near-field diffraction effects and anomalous correlations play an important role. Comparison with a recent theoretical approach described by Imambekov et al. yields good agreement with our experimental results and shows that density correlations can be used for thermometry of quasicondensates.
Interferometry with ultracold atoms promises the possibility of ultraprecise and ultrasensitive m... more Interferometry with ultracold atoms promises the possibility of ultraprecise and ultrasensitive measurements in many fields of physics, and is the basis of our most precise atomic clocks. Key to a high sensitivity is the possibility to achieve long measurement times and precise readout. Ultracold atoms can be precisely manipulated at the quantum level and can be held for very long times in traps; they would therefore be an ideal setting for interferometry. In this paper, we discuss how the nonlinearities from atom-atom interactions, on the one hand, allow us to efficiently produce squeezed states for enhanced readout and, on the other hand, result in phase diffusion that limits the phase accumulation time. We find that low-dimensional geometries are favorable, with two-dimensional (2D) settings giving the smallest contribution of phase diffusion caused by atom-atom interactions. Even for time sequences generated by optimal control, the achievable minimal detectable interaction energy 1E min is of the order of 10 4 µ, where µ is the chemical potential of the Bose-Einstein condensate (BEC) in the trap. From these we have to conclude that for more precise measurements with atom interferometers, more sophisticated strategies, or turning off the interaction-induced dephasing during the phase accumulation stage, will be necessary.
ABSTRACT In this paper we compare two different excitation schemes of rubidium gas-cell frequency... more ABSTRACT In this paper we compare two different excitation schemes of rubidium gas-cell frequency standard. The first scheme is based on the one laser optical pumping and the second scheme is based on the “two-lasers” optical pumping firstly proposed by J. Deng for light shift compensation. We present stability estimations for both schemes supposing that the gas cell has 15 mb of N2 and the laser line width is about 100 MHz. Our calculations do not show the expected significant improvement of the stability in the case of “two-lasers” scheme. This result is connected to the broadening of the absorption line. To avoid this broadening one needs to use a buffer gas pressure around 1 mb and a laser line width of 10 MHz or less.
ABSTRACT Understanding relaxation processes is an important unsolved problem in many areas of phy... more ABSTRACT Understanding relaxation processes is an important unsolved problem in many areas of physics. This fact is exacerbated by the scarcity of experimental tools for characterizing complex transient states. We employ measurements of full quantum mechanical probability distributions of matter-wave interference to study the relaxation dynamics of a coherently split one-dimensional Bose gas and obtain unprecedented information about the dynamical states of the system. Following an initial rapid evolution, the full distributions reveal the approach towards a thermal-like steady state which exhibits an effective temperature eight times lower than the initial equilibrium temperature of the system as well as a strong memory of the initial state prepared by the splitting process. We associate this thermal-like state with pre-thermalization.
We examine the possibility of coherent, reversible information transfer between solid-state super... more We examine the possibility of coherent, reversible information transfer between solid-state superconducting qubits and ensembles of ultra-cold atoms. Strong coupling between these systems is mediated by a microwave transmission line resonator that interacts near-resonantly with the atoms via their optically excited Rydberg states. The solid-state qubits can then be used to implement rapid quantum logic gates, while collective metastable states of the atoms can be employed for long-term storage and optical read-out of quantum information.
We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable ... more We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distribution function of the two-point phase correlation. Comparison to a stochastic model allows to measure the coupling strength and temperature and hence a full characterization of the system.
We propose a novel approach to all-optical frequency standard design, based on a counterintuitive... more We propose a novel approach to all-optical frequency standard design, based on a counterintuitive combination of the coherent population trapping effect and signal discrimination at the maximum of absorption for the probe radiation. The short-term stability of such a standard can achieve the level of 10 −14 / √ τ . The physics beyond this approach is dark resonance splitting caused by interaction of the nuclear magnetic moment with the external magnetic field. PACS numbers: 06.30.Ft, 42.50.Gy, 32.80.Bx The unit of time in the Système International (the second) is defined via the period of the transition between the hyperfine (HF) components of the ground state of the 133 Cs atom (in the limit of vanishing external perturbations). Secondary standards may use other elements (alkali metals, hydrogen). Operation of a frequency standard is provided by locking a microwave signal produced by a quartz crystal oscillator to a resonance on the transition between the working levels [1], i. e. the Zeeman components of the HF structure with zero projection of the total angular momentum. Such a choice of the working levels is dictated by the absence of the linear Zeeman shift. The resonance can be excited by direct microwave transition or by two-photon Raman transition. The latter option provides the basis for all-optical frequency standards where the setup includes no microwave cavities, but electro-optical modulation of the laser beam or direct modulation of the diode laser current are used instead If the interaction time of an atom with the laser field exceeds few optical pumping cycles then the coherent population trapping (CPT) sets in, giving rise to the socalled dark resonance [9, 10]. The physical reason for the CPT is optical pumping of atoms into a coherent superposition of the two ground state sublevels, which is immune to excitation by the frequency-split laser radiation. The CPT leads to decrease of absorption of the laser light. However, if the Raman detuning (the difference between the frequency splitting of the two-component laser radiation and the transition frequency between the two ground state sublevels) exceeds the dark resonance width (what can be as small as few dozens Hz [6, 11]), the CPT atomic state is destroyed, and usual value of the laser radiation absorption is restored.
We measure the two-point density correlation function of freely expanding quasicondensates in the... more We measure the two-point density correlation function of freely expanding quasicondensates in the weakly interacting quasi-one-dimensional (1D) regime. While initially suppressed in the trap, density fluctuations emerge gradually during expansion as a result of initial phase fluctuations present in the trapped quasicondensate. Asymptotically, they are governed by the thermal coherence length of the system. Our measurements take place in an intermediate regime where density correlations are related to near-field diffraction effects and anomalous correlations play an important role. Comparison with a recent theoretical approach described by Imambekov et al. yields good agreement with our experimental results and shows that density correlations can be used for thermometry of quasicondensates.
Interferometry with ultracold atoms promises the possibility of ultraprecise and ultrasensitive m... more Interferometry with ultracold atoms promises the possibility of ultraprecise and ultrasensitive measurements in many fields of physics, and is the basis of our most precise atomic clocks. Key to a high sensitivity is the possibility to achieve long measurement times and precise readout. Ultracold atoms can be precisely manipulated at the quantum level and can be held for very long times in traps; they would therefore be an ideal setting for interferometry. In this paper, we discuss how the nonlinearities from atom-atom interactions, on the one hand, allow us to efficiently produce squeezed states for enhanced readout and, on the other hand, result in phase diffusion that limits the phase accumulation time. We find that low-dimensional geometries are favorable, with two-dimensional (2D) settings giving the smallest contribution of phase diffusion caused by atom-atom interactions. Even for time sequences generated by optimal control, the achievable minimal detectable interaction energy 1E min is of the order of 10 4 µ, where µ is the chemical potential of the Bose-Einstein condensate (BEC) in the trap. From these we have to conclude that for more precise measurements with atom interferometers, more sophisticated strategies, or turning off the interaction-induced dephasing during the phase accumulation stage, will be necessary.
ABSTRACT In this paper we compare two different excitation schemes of rubidium gas-cell frequency... more ABSTRACT In this paper we compare two different excitation schemes of rubidium gas-cell frequency standard. The first scheme is based on the one laser optical pumping and the second scheme is based on the “two-lasers” optical pumping firstly proposed by J. Deng for light shift compensation. We present stability estimations for both schemes supposing that the gas cell has 15 mb of N2 and the laser line width is about 100 MHz. Our calculations do not show the expected significant improvement of the stability in the case of “two-lasers” scheme. This result is connected to the broadening of the absorption line. To avoid this broadening one needs to use a buffer gas pressure around 1 mb and a laser line width of 10 MHz or less.
ABSTRACT Understanding relaxation processes is an important unsolved problem in many areas of phy... more ABSTRACT Understanding relaxation processes is an important unsolved problem in many areas of physics. This fact is exacerbated by the scarcity of experimental tools for characterizing complex transient states. We employ measurements of full quantum mechanical probability distributions of matter-wave interference to study the relaxation dynamics of a coherently split one-dimensional Bose gas and obtain unprecedented information about the dynamical states of the system. Following an initial rapid evolution, the full distributions reveal the approach towards a thermal-like steady state which exhibits an effective temperature eight times lower than the initial equilibrium temperature of the system as well as a strong memory of the initial state prepared by the splitting process. We associate this thermal-like state with pre-thermalization.
We examine the possibility of coherent, reversible information transfer between solid-state super... more We examine the possibility of coherent, reversible information transfer between solid-state superconducting qubits and ensembles of ultra-cold atoms. Strong coupling between these systems is mediated by a microwave transmission line resonator that interacts near-resonantly with the atoms via their optically excited Rydberg states. The solid-state qubits can then be used to implement rapid quantum logic gates, while collective metastable states of the atoms can be employed for long-term storage and optical read-out of quantum information.
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Papers by I. Mazets