M. H. G. de Miranda

University of Colorado, Denver, CO, United States

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Publications (27)177.92 Total impact

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    ABSTRACT: Ultracold polar molecular quantum gases promise to open new research directions ranging from the study of ultra-cold chemistry, precision measurements to novel quantum phase transitions. Based on the preparation of high-phase space density gases of polar KRb molecules in the works of Ni et. al, the authors discussed the control of dipolar collisions and chemical reactions of polar molecules in a regime where quantum statistics, single scattering partial waves, and quantum threshold laws play a dominant role. In particular, the crucial role of electric dipole-dipole interactions and external confinement in determining the chemical reaction rate was pointed out. Finally, the prospects of reaching quantum degeneracy in bi-alkali samples of polar molecules and prospects for these systems as novel dipolar quantum many-body systems were discussed.
    01/2011;
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    ABSTRACT: Chemical reaction rates often depend strongly on stereodynamics, namely the orientation and movement of molecules in three-dimensional space. An ultracold molecular gas, with a temperature below 1 uK, provides a highly unusual regime for chemistry, where polar molecules can easily be oriented using an external electric field and where, moreover, the motion of two colliding molecules is strictly quantized. Recently, atom-exchange reactions were observed in a trapped ultracold gas of KRb molecules. In an external electric field, these exothermic and barrierless bimolecular reactions, KRb+KRb -> K2+Rb2, occur at a rate that rises steeply with increasing dipole moment. Here we show that the quantum stereodynamics of the ultracold collisions can be exploited to suppress the bimolecular chemical reaction rate by nearly two orders of magnitude. We use an optical lattice trap to con?fine the fermionic polar molecules in a quasi-two-dimensional, pancake-like geometry, with the dipoles oriented along the tight confinement direction. With the combination of sufficiently tight confinement and Fermi statistics of the molecules, two polar molecules can approach each other only in a "side-by-side" collision, where the chemical reaction rate is suppressed by the repulsive dipole-dipole interaction. We show that the suppression of the bimolecular reaction rate requires quantum-state control of both the internal and external degrees of freedom of the molecules. The suppression of chemical reactions for polar molecules in a quasi-two-dimensional trap opens the way for investigation of a dipolar molecular quantum gas. Because of the strong, long-range character of the dipole-dipole interactions, such a gas brings fundamentally new abilities to quantum-gas-based studies of strongly correlated many-body physics, where quantum phase transitions and new states of matter can emerge.
    Nature Physics 10/2010; · 19.35 Impact Factor
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    ABSTRACT: Ultracold polar molecules offer the possibility of exploring quantum gases with interparticle interactions that are strong, long-range and spatially anisotropic. This is in stark contrast to the much studied dilute gases of ultracold atoms, which have isotropic and extremely short-range (or 'contact') interactions. Furthermore, the large electric dipole moment of polar molecules can be tuned using an external electric field; this has a range of applications such as the control of ultracold chemical reactions, the design of a platform for quantum information processing and the realization of novel quantum many-body systems. Despite intense experimental efforts aimed at observing the influence of dipoles on ultracold molecules, only recently have sufficiently high densities been achieved. Here we report the experimental observation of dipolar collisions in an ultracold molecular gas prepared close to quantum degeneracy. For modest values of an applied electric field, we observe a pronounced increase in the loss rate of fermionic potassium-rubidium molecules due to ultracold chemical reactions. We find that the loss rate has a steep power-law dependence on the induced electric dipole moment, and we show that this dependence can be understood in a relatively simple model based on quantum threshold laws for the scattering of fermionic polar molecules. In addition, we directly observe the spatial anisotropy of the dipolar interaction through measurements of the thermodynamics of the dipolar gas. These results demonstrate how the long-range dipolar interaction can be used for electric-field control of chemical reaction rates in an ultracold gas of polar molecules. Furthermore, the large loss rates in an applied electric field suggest that creating a long-lived ensemble of ultracold polar molecules may require confinement in a two-dimensional trap geometry to suppress the influence of the attractive, 'head-to-tail', dipolar interactions.
    Nature 04/2010; 464(7293):1324-8. · 38.60 Impact Factor
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    ABSTRACT: We demonstrate a scheme for direct absorption imaging of an ultracold ground-state polar molecular gas near quantum degeneracy. A challenge in imaging molecules is the lack of closed optical cycling transitions. Our technique relies on photon shot-noise limited absorption imaging on a strong bound-bound molecular transition. We present a systematic characterization of this imaging technique. Using this technique combined with time-of-flight (TOF) expansion, we demonstrate the capability to determine momentum and spatial distributions for the molecular gas. We anticipate that this imaging technique will be a powerful tool for studying molecular quantum gases. Comment: 4 pages, 4 figures
    Physical Review A 03/2010; · 3.04 Impact Factor
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    ABSTRACT: We have studied dipolar collisions in an ultracold molecular gas prepared close to quantum degeneracy [1]. By applying a modest external electric field to fermionic KRb molecules produced in a single quantum state, we tune the dipolar interaction strength in the molecular gas. We observe a steep power law dependence of the chemical reaction rate on the induced dipole moment. In addition, we directly observe the spatial anisotropy of the dipolar interactions manifested in measurements of the thermodynamics of the dipolar gas.[4pt] [1] K-K. Ni et al., arXiv:1001.2809 (2010)
    03/2010;
  • B. Neyenhuis, D. Wang, M. H. G. de Miranda, A. Chotia, J. Ye, D. S. Jin
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    ABSTRACT: We report on our ongoing studies of dipolar interactions in ground-state KRb molecules prepared in the quantum regime. At large dipole moment we see a dramatic increase in the inelastic scattering rate due to attractive head-to-tail interactions between molecules [1]. To suppress this inelastic loss we are preparing a gas of polar molecules in a 2D confined geometry provided by a one-dimensional optical lattice. We will explore the effect of the 2D confinement on the lifetime of the trapped molecule gas. [4pt] [1] K.-K. Ni, S. Ospelkaus, D. Wang, G. Quemener, B. Neyenhuis, M. H. G. de Miranda, J. L. Bohn, J. Ye, D. S. Jin, Dipolar collisions of polar molecules in the quantum regime. arXiv:1001.2809.
    03/2010;
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    ABSTRACT: Ultracold fermionic polar molecules of ^40K^87Rb in their absolute rovibronic anf hyperfine state [1] have been recently created in a magnetic trap. This enables experiments to probe ultracold molecular chemistry of polar molecules [2] in well defined quantum states. In addition, KRb molecules are polar and can be manipulated by an electric field. We present theoretical predictions for ultracold dipolar collisions of indistinguishable KRb molecules in a presence of an electric field, using a simple Quantum Threshold model (QT model) [3]. We demonstrate that the KRb + KRb -> K2 + Rb2 chemical reaction rate increases as the sixth power of the dipole moment induced by the electric field for fermionic KRb isotopes. We also estimate the temperature dependence of the chemical rates in zero electric field. These predictions are in excellent agreement with experimental data [2,4]. [1] Ni et al., Science 322, 231 (2008) ; Ospelkaus et al., Phys. Rev. Lett. 104, 030402 (2010). [2] Ospelkaus et al., arXiv:0912.3854, Science, in press (2010). [3] Qu'em'ener et al., Phys. Rev. A, in press (2010). [4] Ni et al., arXiv:1001.2809, submitted (2010).
    03/2010;
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    ABSTRACT: We prepare a near-quantum-degenerate gas of fermionic KRb molecules, with all the molecules in the absolute lowest energy state. We observe atom-exchange chemical reactions in a regime where the reaction rates are determined by the quantum statistics of the molecules, single partial wave scattering, and quantum threshold laws [1].[4pt] [1] S. Ospelkaus, K.-K. Ni, D. Wang, M. H. G. de Miranda, B. Neyenhuis, G. Qu'em'ener, P. S. Julienne, J. L. Bohn, D. S. Jin, J. Ye, Quantum-State Controlled Chemical Reactions of Ultracold KRb Molecules, Science (in press).
    03/2010;
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    ABSTRACT: How does a chemical reaction proceed at ultralow temperatures? Can simple quantum mechanical rules such as quantum statistics, single partial-wave scattering, and quantum threshold laws provide a clear understanding of the molecular reactivity under a vanishing collision energy? Starting with an optically trapped near-quantum-degenerate gas of polar 40K87Rb molecules prepared in their absolute ground state, we report experimental evidence for exothermic atom-exchange chemical reactions. When these fermionic molecules were prepared in a single quantum state at a temperature of a few hundred nanokelvin, we observed p-wave-dominated quantum threshold collisions arising from tunneling through an angular momentum barrier followed by a short-range chemical reaction with a probability near unity. When these molecules were prepared in two different internal states or when molecules and atoms were brought together, the reaction rates were enhanced by a factor of 10 to 100 as a result of s-wave scattering, which does not have a centrifugal barrier. The measured rates agree with predicted universal loss rates related to the two-body van der Waals length.
    Science 02/2010; 327(5967):853-7. · 31.20 Impact Factor
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    ABSTRACT: We report the preparation of a rovibronic ground-state molecular quantum gas in a single hyperfine state and, in particular, the absolute lowest quantum state. This addresses the last internal degree of freedom remaining after the recent production of a near quantum degenerate gas of molecules in their rovibronic ground state, and provides a crucial step towards full control over molecular quantum gases. We demonstrate a scheme that is general for bialkali polar molecules and allows the preparation of molecules in a single hyperfine state or in an arbitrary coherent superposition of hyperfine states. The scheme relies on electric-dipole, two-photon microwave transitions through rotationally excited states and makes use of electric nuclear quadrupole interactions to transfer molecular population between different hyperfine states.
    Physical Review Letters 01/2010; 104(3):030402. · 7.73 Impact Factor
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    ABSTRACT: How does a chemical reaction proceed at ultralow temperatures? Can simple quantum mechanical rules such as quantum statistics, single scattering partial waves, and quantum threshold laws provide a clear understanding for the molecular reactivity under a vanishing collision energy? Starting with an optically trapped near quantum degenerate gas of polar $^{40}$K$^{87}$Rb molecules prepared in their absolute ground state, we report experimental evidence for exothermic atom-exchange chemical reactions. When these fermionic molecules are prepared in a single quantum state at a temperature of a few hundreds of nanoKelvins, we observe p-wave-dominated quantum threshold collisions arising from tunneling through an angular momentum barrier followed by a near-unity probability short-range chemical reaction. When these molecules are prepared in two different internal states or when molecules and atoms are brought together, the reaction rates are enhanced by a factor of 10 to 100 due to s-wave scattering, which does not have a centrifugal barrier. The measured rates agree with predicted universal loss rates related to the two-body van der Waals length.
    12/2009;
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    ABSTRACT: We have produced near quantum degenerate ^40K^87Rb polar molecules in their rovibrational ground state using magneto-association followed by STIRAP transfer. Preliminary measurements show that trap lifetime of these fermion molecules is limited to ˜ 100 ms. We are investigating the KRb loss in the presence of either K or Rb atoms to look for evidence of chemical reactions at ultracold temperatures. This work is supported by the NSF and NIST.
    05/2009;
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    ABSTRACT: We report the creation and characterization of a near quantum-degenerate gas of polar 40K-87Rb molecules in their absolute rovibrational ground state. Starting from weakly bound heteronuclear KRb Feshbach molecules, we implement precise control of the molecular electronic, vibrational, and rotational degrees of freedom with phase-coherent laser fields. In particular, we coherently transfer these weakly bound molecules across a 125 THz frequency gap in a single step into the absolute rovibrational ground state of the electronic ground potential. Phase coherence between lasers involved in the transfer process is ensured by referencing the lasers to two single components of a phase-stabilized optical frequency comb. Using these methods, we prepare a dense gas of 4 x 10(4) polar molecules at a temperature below 400 nK. This fermionic molecular ensemble is close to quantum degeneracy and can be characterized by a degeneracy parameter of T/T(F) = 3. We have measured the molecular polarizability in an optical dipole trap where the trap lifetime gives clues to interesting decay mechanisms. Given the large measured dipole moment of the KRb molecules of 0.5 Debye, the study of quantum degenerate molecular gases interacting via strong dipolar interactions is now within experimental reach. PACS numbers: 37.10.Mn, 37.10.Pq.
    Faraday Discussions 01/2009; 142:351-9; discussion 429-61. · 3.82 Impact Factor
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    ABSTRACT: A quantum gas of ultracold polar molecules, with long-range and anisotropic interactions, not only would enable explorations of a large class of many-body physics phenomena but also could be used for quantum information processing. We report on the creation of an ultracold dense gas of potassium-rubidium (40K87Rb) polar molecules. Using a single step of STIRAP (stimulated Raman adiabatic passage) with two-frequency laser irradiation, we coherently transfer extremely weakly bound KRb molecules to the rovibrational ground state of either the triplet or the singlet electronic ground molecular potential. The polar molecular gas has a peak density of 10(12) per cubic centimeter and an expansion-determined translational temperature of 350 nanokelvin. The polar molecules have a permanent electric dipole moment, which we measure with Stark spectroscopy to be 0.052(2) Debye (1 Debye = 3.336 x 10(-30) coulomb-meters) for the triplet rovibrational ground state and 0.566(17) Debye for the singlet rovibrational ground state.
    Science 10/2008; 322(5899):231-5. · 31.20 Impact Factor
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    ABSTRACT: We report on the improved characterization and operation of an optical frequency standard based on nuclear-spin-polarized, ultracold neutral strontium confined in a one dimensional optical lattice. We implement a remote optical carrier phase link between JILA and NIST Boulder Campus, permitting high precision evaluation of the Sr system with other optical standards. Frequency measurement against a free-space Ca standard enables determination of systematic shifts of the Sr standard at or below 1x10<sup>−16</sup> fractional uncertainty. We observe a density-dependent shift of the clock transition and its dependence on excited state fraction, with a zero crossing of the shift. We perform a 50-hour-long absolute frequency measurement of the strontium transition referenced to the NIST-F1 Cs fountain standard. This yields a value for the Sr clock transition frequency with a fractional uncertainty of 8.6x10<sup>−16</sup>, limited by the H-maser and Cs standards used. This represents our fifth, and the most accurate, measurement of the <sup>87</sup>Sr clock frequency.
    Frequency Control Symposium, 2008 IEEE International; 06/2008
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    M J Thorpe, F Adler, K C Cossel, M H G Miranda, J Ye
    Chemical Physics Letters 05/2008; 468(1-3):1-8. · 2.15 Impact Factor
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    ABSTRACT: We present experimental efforts toward the creation of ultracold gas of KRb polar molecules. We start by creating extremely weakly bound molecules using a magnetic-field Feshbach resonance. This ultracold dense sample of Feshbach molecules provides a starting point for coherent optical transfer schemes aimed at creating tightly bound, polar molecules. Starting with Feshbach molecules, we have performed two-photon and one-photon spectroscopy. We have also demonstrated coherent optical transfer of Feshbach molecules to a more deeply bound state in the electronic ground state. We will discuss suitable routes to extend this work to even more deeply bound vibrational levels where the molecules can have a significant electric dipole moment.
    05/2008;
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    ABSTRACT: We have recently demonstrated coherent optical transfer of KRb Feshbach molecules to a more deeply bound vibrational state. This transfer relied on an extensive search for a suitable intermediate state of KRb* as well as precision two-photon spectroscopy of target vibrational levels in the electronic ground-state KRb. We will present results of the KRb and KRb* spectroscopy as well as our progress toward creation of degenerate KRb polar molecules.
    05/2008;
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    ABSTRACT: The absolute frequency of the 1S0-3P0 clock transition of 87Sr has been measured to be 429 228 004 229 873.65 (37) Hz using lattice-confined atoms, where the fractional uncertainty of 8.6x10-16 represents one of the most accurate measurements of an atomic transition frequency to date. After a detailed study of systematic effects, which reduced the total systematic uncertainty of the Sr lattice clock to 1.5x10-16, the clock frequency is measured against a hydrogen maser which is simultaneously calibrated to the US primary frequency standard, the NIST Cs fountain clock, NIST-F1. The comparison is made possible using a femtosecond laser based optical frequency comb to phase coherently connect the optical and microwave spectral regions and by a 3.5 km fiber transfer scheme to compare the remotely located clock signals.
    Metrologia 04/2008; · 1.90 Impact Factor
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    ABSTRACT: Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies. Rigorous evaluations of these clocks require direct comparisons between them. We have realized a high-performance remote comparison of optical clocks over kilometer-scale urban distances, a key step for development, dissemination, and application of these optical standards. Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1 x 10(-16) fractional level, surpassing the current best evaluations of cesium (Cs) primary standards. We also report on the observation of density-dependent effects in the spin-polarized fermionic sample and discuss the current limiting effect of blackbody radiation-induced frequency shifts.
    Science 04/2008; 319(5871):1805-8. · 31.20 Impact Factor

Publication Stats

2k Citations
177.92 Total Impact Points

Institutions

  • 2010
    • University of Colorado
      • Department of Physics
      Denver, CO, United States
  • 2008–2010
    • University of Colorado at Boulder
      • Department of Physics
      Boulder, CO, United States
  • 2008–2009
    • National Institute of Standards and Technology
      • • Quantum Physics Division
      • • Time and Frequency Division
      Gaithersburg, MD, United States