Peyman Ahmadi

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (35)49.79 Total impact

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    ABSTRACT: We report on the formation of ultracold weakly bound Feshbach molecules of 23Na40K, the first fermionic molecule that is chemically stable in its absolute ground state. The lifetime of the nearly degenerate molecular gas exceeds 100 ms in the vicinity of the Feshbach resonance. The measured dependence of the molecular binding energy on the magnetic field demonstrates the open-channel character of the molecules over a wide field range and implies significant singlet admixture. This will enable efficient transfer into the singlet vibrational ground state, resulting in a stable molecular Fermi gas with strong dipolar interactions.
    Physical Review Letters 08/2012; 109(8). · 7.73 Impact Factor
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    ABSTRACT: We have created a quantum degenerate Bose-Fermi mixture of ^23Na and ^40K with widely tunable interactions via broad interspecies Feshbach resonances. Over thirty Feshbach resonances between ^23Na and ^40K were identified, including p-wave multiplet resonances. Observed broad Feshbach resonances opens up a path to study the fate of an impurity interacting with its environment, a fundamental problem in condensed matter physics. We study the interaction of an impurity immersed in a Bose-Einstein condensate of ^23Na. We perform radio-frequency spectroscopy on the impurity atom and the bath, which is expected to probe the spectral features characteristic for polaronic dressing: A delta-like peak in addition to a broad pedestal coming from the interactions between the impurity and the phonons in the condensate. Our system, with its widely tunable interactions, promises to be an ideal system to study the evolution from Bose polarons to Fermi polarons as the imbalance between ^23Na and ^40K is varied.
    06/2012;
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    ABSTRACT: The fate of an impurity interacting with its environment is a fundamental problem in condensed matter physics. The famous example is that of an electron moving in the crystal background of ions, dressing itself with lattice distortions, phonons. In ultracold atomic systems, impurities interacting with a Fermi sea have been studied, leading to the observation of Fermi polarons. Here we study the interaction of an impurity immersed in a Bose-Einstein condensate of ^23Na. We perform radio-frequency spectroscopy on the impurity atom and the bath, which is expected to probe the spectral features characteristic for polaronic dressing: A delta-like peak in addition to a broad pedestal coming from the interactions between the impurity and the phonons in the condensate. A mixture of ^23Na and ^40K with its widely tunable interactions promises to be an ideal system to study the evolution from Bose polarons to Fermi polarons as the imbalance between ^23Na and ^40K is varied.
    06/2012;
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    ABSTRACT: We have created a quantum degenerate Bose-Fermi mixture of 23Na and 40K with widely tunable interactions via broad interspecies Feshbach resonances. Twenty Feshbach resonances between 23Na and 40K were identified. The large and negative triplet background scattering length between 23Na and 40K causes a sharp enhancement of the fermion density in the presence of a Bose condensate. As explained via the asymptotic bound-state model (ABM), this strong background scattering leads to a series of wide Feshbach resonances observed at low magnetic fields. Our work opens up the prospect to create chemically stable, fermionic ground state molecules of 23Na-40K where strong, long-range dipolar interactions will set the dominant energy scale.
    Physical Review A 10/2011; · 3.04 Impact Factor
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    ABSTRACT: We have created a triply quantum degenerate mixture of bosonic $^{41}$K and two fermionic species $^{40}$K and $^6$Li. The boson is shown to be an efficient coolant for the two fermions, spurring hopes for the observation of fermionic superfluids with imbalanced masses. We observe multiple heteronuclear Feshbach resonances, in particular a wide s-wave resonance for the combination $^{41}$K-$^{40}$K, opening up studies of strongly interacting {\it isotopic} Bose-Fermi mixtures. For large imbalance, we enter the polaronic regime of dressed impurities immersed in a bosonic or fermionic bath.
    Physical Review A 03/2011; 84(1). · 3.04 Impact Factor
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    ABSTRACT: We report the observation of a triply quantum degenerate mixture of ^41K, ^40K and ^6Li atoms. It is demonstrated that bosonic ^41K atom is an efficient coolant for sympathetic cooling of fermionic ^40K and ^6Li atoms. The ^40K and ^6Li mixture provides access to a strongly correlated Fermi-Fermi mixture allowing us to study superfluidity and Cooper pairing with imbalanced masses. We also present our investigation of ^41K and ^40K, a Bose-Fermi mixture where a 12 G p-wave resonance and a 40 G s-wave resonance are observed. Negligible differential gravitational sag between ^41K and ^40K makes these resonances excellent candidates for studying unexplored properties of Bose-Fermi mixtures such as Boson mediated Cooper pairing.
    03/2011;
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    ABSTRACT: Strongly interacting mixtures of unequal fermionic species promise to allow access to novel states of matter, such as Cooper pairing without time-reversal symmetry, the FFLO (Fulde-Ferrell-Larkin- Ovchinnikov) state of Cooper pairs at finite momenta, and a basic form of quark (color) superfluidity. We will present our experiments on cooling a Fermi-Fermi mixture of the fermionic Alkalis ^6Li and ^40K. The difficulty of the low natural abundance of ^40K (%0.01) is typically overcome with the use of enriched, but expensive, ^40K. In our approach we use two independent Zeeman slowers optimized for high atomic fluxes of non-enriched K and Li. This allows us to load 5 x 10^7 fermionic K into a magneto-optical trap, and it also gives us access to the bosonic isotopes of ^39K and ^41K as possible sympathetic coolants for both ^6Li and ^40K. As a crucial step, we have produced a Bose-Einstein condensate of ^41K by direct evaporation and we were able to sympathetically cool the fermion ^40K. Our immediate goal is the production of a degenerate Fermi-Fermi mixture of ^6Li and ^40K.
    03/2010;
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    ABSTRACT: The study of mixtures of two or more different atomic species is a new frontier in the field of ultracold quantum gases. Part of the motivation for this research lies in the interest in novel forms of superfluidity, which could for example mimic bulk nuclear matter and exotic superconductors. In this poster, we will present our experimental progress on cooling a Fermi-Fermi mixture of the fermionic Alkalis ^6Li and ^40K. The difficulty of the low natural abundance of ^40K (%0.01) is typically overcome with the use of enriched, but expensive, ^40K. In our approach we use two independent Zeeman slowers optimized for high atomic fluxes of non-enriched K and Li. This allows us to load 5 x 10^7 fermionic K into a magneto-optical trap, and it also gives us access to the bosonic isotopes of ^39K and ^41K as possible sympathetic coolants for both ^6Li and ^40K. After producing a Bose-Einstein condensate of ^41K by direct evaporation and sympathetically cooling the fermion ^40K, our next goal is the production of a degenerate Fermi-Fermi mixture of ^6Li and ^40K.
    03/2010;
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    ABSTRACT: We report the observation of high-order resonances of the quantum δ-kicked accelerator using a BEC kicked by a standing wave of light. The signature of these resonances is the existence of quantum accelerator modes. For the first time quantum accelerator modes were seen near 1/2, 2/3 and 1/3 of the half-Talbot time. Using a BEC enabled the internal momentum state structure of the modes and resonances to be studied for the first time. This structure has many similarities to that present in the fractional Talbot effect. We present a theory for this system based on rephasing of momentum orders and apply it to predict the behavior of the accelerator modes around a resonance of any order.
    EPL (Europhysics Letters) 02/2010; 89(3):33001. · 2.26 Impact Factor
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    ABSTRACT: We investigate the creation mechanism of quantum accelerator modes which are attributed to the existence of the stability islands in an underlying pseudoclassical phase space of the quantum delta-kicked accelerator. Quantum accelerator modes can be created by exposing a Bose-Einstein condensate to a pulsed standing light wave. We show that constructive interference between momentum states populated by the pulsed light determines the stability island’s existence in the underlying pseudoclassical phase space. We generalize this interference model to incorporate higher-order accelerator modes, showing that they are generated if the rephasing occurs after multiple pulses. The model is extended to predict the momentum structure of the quantum accelerator modes close to higher-order quantum resonances. These predictions are in good agreement with our experimental observations.
    Physical Review A 11/2009; · 3.04 Impact Factor
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    ABSTRACT: We realize the production of an array of 10-30 independent ^87Rb spin-1 BECs in the standing wave potential of a CO2 laser by extending the single focus trap geometry of our all-optical BEC to a one-dimensional lattice. The period of the optical lattice created by the CO2 laser is 5.3mum and is therefore large enough to optically resolve the individual sites and to selectively address them. By applying a high magnetic field gradient, we are able to manipulate single sites using microwave transitions between the different hyperfine states. We will present our experimental data together with theoretical simulations and discuss applications to studies of small condensates and their interactions.
    05/2009;
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    ABSTRACT: In what forms does matter organize itself under the influence of interaction? This is the fundamental question of many-body physics, which arises at all length scales: from the dense quark matter present in the beginning of our Universe, to the atomic nucleus, the electrons inside a metal, and the inner workings of a neutron star. However, strong interactions between particles do not allow for a simple description of such systems. Strongly interacting mixtures of ultracold atoms will allow us to realize complex many-body systems relevant to the description of High-TC and Giant Magnetoresistance materials and which cannot be simulated theoretically. We are constructing a new apparatus that will allow to cool three different species of atoms, two of them fermionic, ^6Li and ^40K, and one of them bosonic, ^23Na. A two-species Fermi-Fermi mixture close to a Feshbach resonance realizes an unusual form of fermionic superfluid with unequal masses. A mass- and number imbalanced Fermi mixture might give access to new states of fermionic matter, such as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase of Cooper pairs with non-zero momentum.
    05/2009;
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    ABSTRACT: We report on the high resolution photoassociation spectroscopy of a $^{87}$Rb spin-1 Bose-Einstein condensate to the $1_\mathrm{g} (P_{3/2}) v = 152$ excited molecular states. We demonstrate the use of spin dependent photoassociation to experimentally identify the molecular states and their corresponding initial scattering channel. These identifications are in excellent agreement with the eigenvalues of a hyperfine-rotational Hamiltonian. Using the observed spectra we estimate the change in scattering length and identify photoassociation laser light frequency ranges that maximize the change in the spin-dependent mean-field interaction energy. Comment: 5 pages, 4 figures
    Physical Review A 06/2008; · 3.04 Impact Factor
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    ABSTRACT: We have realized a one dimensional optical lattice for individual atoms with a lifetime >300 s, which is 5 times longer than previously reported. In order to achieve this long lifetime, it is necessary to laser cool the at-oms briefly every 20 s to overcome heating due to technical fluctuations in the trapping potential. Without cooling, we observe negligible atom loss within the first 20 s followed by an exponential decay with a 62 s time constant. We obtain quantitative agreement with the measured fluctuations of the trapping potential and the corresponding theoretical heating rates. Comment: 4 pages, 5 figures
    Physical Review A 05/2008; · 3.04 Impact Factor
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    ABSTRACT: Individual atoms are delivered to a high-finesse optical cavity using an optical conveyor. Strong coupling of the atom with the cavity allows cooling and detection of atoms for up to 15 s.
    05/2008;
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    ABSTRACT: We report on the high resolution (5 MHz) photoassociation spectroscopy of ^87Rb spin-1 BEC to the 1g (P3/2) v=152 excited molecular state manifold. Using a combination of dipole selection rules, collision channel analysis and rotational progression of the spectrum we identify total molecular angular momentum, F, and total molecular nuclear spin, I, for the observed states. These identifications are compared to a hyperfine-rotational Hamiltonian [1] for Hund's case (c). We find a good agreement to the predicted lines. The eigenvalues of this Hamiltonian was used to predict further weak lines which their existence are confirmed experimentally. In conclusion, we demonstrate the use of spin dependent photoassociation to experimentally identify hyperfine-rotational structure of the molecular states with sufficiently high resolution. These studies will improve current understanding of the hyperfine-rotation molecular potentials in Hund's case (c). [1] X.T. Wang, et al., Phys. Rev. A. 57, 4600 (1998).
    05/2008;
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    ABSTRACT: A quantum d-kicked accelerator exhibits the phenomenon of resonance whenever the period of kicking is a rational fraction of the half-Talbot time similar to a quantum d-kicked rotor. The signatures of these resonances are the existence of quantum accelerator modes. We observed resonances for the periods of 1/2, 2/3, and 1/3 of the half-Talbot time. A model based on the rephasing of the momentum states constituting the accelerator modes has been successfully used to predict the behavior.
    05/2008;
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    ABSTRACT: Cavity QED systems consisting of neutral atoms coupled to high-finesse optical micro-cavities have important applications to quantum information processing. We have developed an experiment with trapped atoms in a high finesse cavity in the strong coupling regime. We have demonstrated deterministic loading and storage of individual atoms delivered from a magneto-optic trap to the resonator using an atom conveyor [1]. We will also discuss future applications. [1] K.M. Fortier et al., Phys. Rev. Lett. 98, 233601 (2007).
    05/2008;
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    ABSTRACT: Individual laser-cooled atoms are delivered on-demand from a single atom magneto-optic trap to a high-finesse optical cavity using an optical conveyor. Strong coupling of the atom with the cavity field allows simultaneous cooling and detection of individual atoms for time scales exceeding 15 s. We demonstrate the ability to manipulate the position of a single atom relative to the cavity mode with excellent control and reproducibility.
    Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 01/2008
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    ABSTRACT: We report the observation of high order resonances of the quantum $\delta$-kicked accelerator using a BEC kicked by a standing wave of light. The signature of these resonances is the existence of quantum accelerator modes. For the first time quantum accelerator modes were seen near 1/4 and 1/3 of the Talbot time. Using a BEC enabled us to study the detailed structure of the modes and resonances which are related to the fractional Talbot effect. We present a general theory for this system and apply it to predict the behavior of the accelerator modes.
    07/2007;

Publication Stats

244 Citations
49.79 Total Impact Points

Institutions

  • 2009–2012
    • Massachusetts Institute of Technology
      • Department of Physics
      Cambridge, Massachusetts, United States
  • 2005–2010
    • Oklahoma State University - Stillwater
      • Department of Physics
      Stillwater, OK, United States
  • 2007–2008
    • Georgia Institute of Technology
      • School of Physics
      Atlanta, GA, United States