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ABSTRACT: We report the laser-cooling and confinement of Cd atoms in a magneto-optical trap, and characterize the loading process from the background Cd vapor. The trapping laser drives the 1S0-1P1 transition at 229 nm in this two-electron atom and also photoionizes atoms directly from the 1P1 state. This photoionization overwhelms the other loss mechanisms and allows a direct measurement of the photoionization cross section, which we measure to be 2(1)x10^(-16)cm^(2) from the 1P1 state. When combined with nearby laser-cooled and trapped Cd^(+) ions, this apparatus could facilitate studies in ultracold interactions between atoms and ions. Comment: 8 pages, 11 figures
06/2007;
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L. Deslauriers,
M. Acton,
B. B. Blinov,
K. -A. Brickman, P. C. Haljan,
W. K. Hensinger,
D. Hucul,
S. Katnik,
Kohn, Jr., R. N,
P. J. Lee,
M. J. Madsen,
P. Maunz,
S. Olmschenk,
D. L. Moehring,
D. Stick,
J. Sterk,
M. Yeo,
K. C. Younge,
C. Monroe
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ABSTRACT: Atomic cadmium ions are loaded into radiofrequency ion traps by
photoionization of atoms in a cadmium vapor with ultrafast laser pulses. The
photoionization is driven through an intermediate atomic resonance with a
frequency-quadrupled mode-locked Ti:Sapphire laser that produces pulses of
either 100 fsec or 1 psec duration at a central wavelength of 229 nm. The large
bandwidth of the pulses photoionizes all velocity classes of the Cd vapor,
resulting in high loading efficiencies compared to previous ion trap loading
techniques. Measured loading rates are compared with a simple theoretical
model, and we conclude that this technique can potentially ionize every atom
traversing the laser beam within the trapping volume. This may allow the
operation of ion traps with lower levels of background pressures and less trap
electrode surface contamination. The technique and laser system reported here
should be applicable to loading most laser-cooled ion species.
09/2006;
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Quantum Information & Computation. 01/2006; 6:465-482.
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ABSTRACT: We report the implementation of Grover's quantum search algorithm in the scalable system of trapped atomic ion quantum bits. Any one of four possible states of a two-qubit memory is marked, and following a single query of the search space, the marked element is successfully recovered with an average probability of 60(2)%. This exceeds the performance of any possible classical search algorithm, which can only succeed with a maximum average probability of 50%. Comment: 4 pages, 3 figures, updated error discussion
10/2005;
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ABSTRACT: A M{\o}lmer-S{\o}rensen entangling gate is realized for pairs of trapped $^{111}$Cd$^+$ ions using magnetic-field insensitive "clock" states and an implementation offering reduced sensitivity to optical phase drifts. The gate is used to generate the complete set of four entangled states, which are reconstructed and evaluated with quantum-state tomography. An average target-state fidelity of 0.79 is achieved, limited by available laser power and technical noise. The tomographic reconstruction of entangled states demonstrates universal quantum control of two ion-qubits, which through multiplexing can provide a route to scalable architectures for trapped-ion quantum computing. Comment: 6 pages, 5 figures
08/2005;
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ABSTRACT: There are several known schemes for entangling trapped ion quantum bits for large-scale quantum computation. Most are based on an interaction between the ions and external optical fields, coupling internal qubit states of trapped-ions to their Coulomb-coupled motion. In this paper, we examine the sensitivity of these motional gate schemes to phase fluctuations introduced through noisy external control fields, and suggest techniques to suppress the resulting phase decoherence. Comment: 21 pages 12 figures
05/2005;
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ABSTRACT: Favored schemes for trapped-ion quantum logic gates use bichromatic laser fields to couple internal qubit states with external motion through a "spin-dependent force." We introduce a new degree of freedom in this coupling that reduces its sensitivity to phase decoherence. We demonstrate bichromatic spin-dependent forces on a single trapped 111Cd+ ion, and show that phase coherence of the resulting entangled states of spin and motion depends critically upon the spectral arrangement of the optical fields. This applies directly to the operation of entangling gates on multiple ions.
Physical Review Letters 05/2005; 94(15):153602. · 7.37 Impact Factor
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ABSTRACT: Favored schemes for trapped-ion quantum logic gates use bichromatic laser fields to couple internal qubit states with external motion through a "spin-dependent force." We introduce a new degree of freedom in this coupling that reduces its sensitivity to phase decoherence. We demonstrate bichromatic spin-dependent forces on a single trapped $^{111}$Cd$^+$ ion, and show that phase coherence of the resulting "Schr\"{o}dinger-cat" states of motion depends critically upon the spectral arrangement of the optical fields. This applies directly to the operation of entangling gates on multiple ions. Comment: 5 pages, 4 figures
11/2004;
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ABSTRACT: We characterize several equilibrium vortex effects in a rotating Bose-Einstein condensate. Specifically we attempt precision measurements of vortex lattice spacing and the vortex core size over a range of condensate densities and rotation rates. These measurements are supplemented by numerical simulations, and both experimental and numerical data are compared to theory predictions of Sheehy and Radzihovsky [17] (cond-mat/0402637) and Baym and Pethick [25] (cond-mat/0308325). Finally, we study the effect of the centrifugal weakening of the trapping spring constants on the critical temperature for quantum degeneracy and the effects of finite temperature on vortex contrast. Comment: Fixed minor notational inconsistencies in figures. 12 pages, 8 figures
05/2004;
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ABSTRACT: We report on ground state laser cooling of single 111Cd+ ions confined in radio-frequency (Paul) traps. Heating rates of trapped ion motion are measured for two different trapping geometries and electrode materials, where no effort was made to shield the electrodes from the atomic Cd source. The low measured heating rates suggest that trapped 111Cd+ ions may be well-suited for experiments involving quantum control of atomic motion, including applications in quantum information science. Comment: 4 pages, 6 figures, Submitted to PRA
04/2004;
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ABSTRACT: We study the formation of large vortex aggregates in a rapidly rotating dilute-gas Bose-Einstein condensate. When we remove atoms from the rotating condensate with a tightly focused, resonant laser, the density can be locally suppressed, while fast circulation of a ring-shaped superflow around the area of suppressed density is maintained. Thus a giant vortex core comprising 7 to 60 phase singularities is formed. The giant core is only metastable, and it will refill with distinguishable single vortices after many rotation cycles. The surprisingly long lifetime of the core can be attributed to the influence of strong Coriolis forces in the condensate. In addition we have been able to follow the precession of off-center giant vortices for more than 20 cycles.
Physical Review Letters 06/2003; 90(17):170405. · 7.37 Impact Factor
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ABSTRACT: We have studied the dynamics of large vortex lattices in a dilute-gas Bose-Einstein condensate. While undisturbed lattices have a regular hexagonal structure, large-amplitude quadrupolar shape oscillations of the condensate are shown to induce a wealth of nonequilibrium lattice dynamics. When exciting an m=-2 mode, we observe shifting of lattice planes, changes of lattice structure, and sheetlike structures in which individual vortices appear to have merged. Excitation of an m=+2 mode dissolves the regular lattice, leading to randomly arranged but still strictly parallel vortex lines.
Physical Review Letters 10/2002; 89(10):100403. · 7.37 Impact Factor
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ABSTRACT: We have developed an evaporative cooling technique that accelerates the rotation of an ultracold 87Rb gas, confined in a static harmonic potential. As a normal gas is evaporatively spun up and cooled below quantum degeneracy, it is found to nucleate vorticity in a Bose-Einstein condensate. Measurements of the condensate's aspect ratio and surface-wave excitations are consistent with effective rigid-body rotation. Rotation rates of up to 94% of the centrifugal limit are inferred. A threshold in the normal cloud's rotation is observed for the intrinsic nucleation of the first vortex. The threshold value lies below the prediction for a nucleation mechanism involving the excitation of surface waves of the condensate.
Physical Review Letters 12/2001; 87(21):210403. · 7.37 Impact Factor
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ABSTRACT: A vortex in a condensate in a nonspherical trapping potential will in general experience a torque. The torque will induce tilting of the direction of the vortex axis. We observe this behavior experimentally and show that by applying small distortions to the trapping potential, we can control the tilting behavior. By suppressing vortex tilt, we have been able to hold the vortex axis along the line of sight for up to 15 sec. Alternatively, we can induce a 180 degrees tilt, effectively reversing the charge on the vortex as observed in the lab frame. We characterize the vortex nondestructively with a surface-wave spectroscopic technique.
Physical Review Letters 05/2001; 86(14):2922-5. · 7.37 Impact Factor
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ABSTRACT: We have created spatial dark solitons in two-component Bose-Einstein condensates in which the soliton exists in one of the condensate components and the soliton nodal plane is filled with the second component. The filled solitons are stable for hundreds of milliseconds. The filling can be selectively removed, making the soliton more susceptible to dynamical instabilities. For a condensate in a spherically symmetric potential, these instabilities cause the dark soliton to decay into stable vortex rings. We have imaged the resulting vortex rings.
Physical Review Letters 05/2001; 86(14):2926-9. · 7.37 Impact Factor
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ABSTRACT: We have observed and characterized the dynamics of singly quantized vortices in dilute-gas Bose-Einstein condensates. Our condensates are produced in a superposition of two internal states of 87Rb, with one state supporting a vortex and the other filling the vortex core. Subsequently, the state filling the core can be partially or completely removed, reducing the radius of the core by as much as a factor of 13, all the way down to its bare value of the healing length. The corresponding superfluid rotation rates, evaluated at the core radius, vary by a factor of 150, but the precession frequency of the vortex core about the condensate axis changes by only a factor of 2.
Physical Review Letters 11/2000; 85(14):2857-60. · 7.37 Impact Factor
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ABSTRACT: Summary form only given. Since the first observations of Bose Einstein condensates (BEC) in dilute atomic gases, there has been considerable interest in observing effects in atomic BEC akin to the hallmark effects associated with a superfluid, in particular persistent, quantized circulation of the fluid. Using a method proposed by Williams and Holland' we have prepared vortices, macroscopic quantum states with quantized angular momentum, in a trapped BEC of /sup 87/Rb. The experimental realization of this method takes advantage of unique features of the time averaged orbiting potential (TOP) trap and builds on earlier work involving two-component condensates. The two components refer to two different internal hyperfine states of /sup 87/Rb, confined by identical and fully overlapping magnetic trap potentials in these experiments.
Quantum Electronics and Laser Science Conference, 2000. (QELS 2000). Technical Digest; 06/2000
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ABSTRACT: We have created vortices in two-component Bose-Einstein condensates. The vortex state was created through a coherent process involving the spatial and temporal control of interconversion between the two components. Using an interference technique, we map the phase of the vortex state to confirm that it possesses angular momentum. We can create vortices in either of the two components and have observed differences in the dynamics and stability. Comment: 4 pages with 3 figures
08/1999;
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ABSTRACT: Summary form only given. Following the first observations of Bose-Einstein condensation (BEC) in dilute atomic gases, there has been considerable interest in multiple condensates as a system of interpenetrating quantum fluids. Most recently in our time averaged orbiting potential (TOP) trap, we have created coherent superpositions of condensates in the |F=1, m<sub>F</sub>=-1> and |F=2, m<sub>F</sub>=1> hyperfine ground states of Rubidium-87. A coupling field connects the states of this two level system. Following evaporative cooling to BEC in the |1,-1> state, a short coupling pulse allows us to transfer an arbitrary proportion of the atoms into the upper |2,1> state. In the first experiments with two component condensates, we have determined the ratio of the intraspecies scattering lengths for the two hyperfine states mentioned above; we have transferred half of the atoms to the upper |2,1> state to investigate the dynamics of the two components separation; and we have found that, in the regions where they overlap, the two condensates retain a well defined phase even after the damping of their relative center of mass motion. To further our studies of double condensates, we have implemented a new, state-sensitive form of nondestructive imaging, a technique first pioneered by Zernike in the field of microscopy, and more recently adapted to the imaging of condensates by the group at MIT. We exploit the state sensitivity of the technique to distinguish the two spin states inside the trap (or, more accurately, to measure their relative density across the cloud)
Quantum Electronics and Laser Science Conference, 1999. QELS '99. Technical Digest. Summaries of Papers Presented at the; 06/1999
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ABSTRACT: The order parameter of a condensate with two internal states can continuously distort in such a way as to remove twists that have been imposed along its length. We observe this effect experimentally in the collapse and recurrence of Rabi oscillations in a magnetically trapped, two-component Bose-Einstein condensate of ^87Rb.
06/1999;
