Zeros of Rydberg–Rydberg Föster interactions

Walker, Thad; Saffman, M.

doi:10.1088/0953-4075/38/2/022

Cited by 85 publications

(94 citation statements)

References 15 publications

(27 reference statements)

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“…This effect can be exploited as an exciton trap for continuous time quantum random walk experiments [9]. It also constitutes another constraint to states that are suited for dipole blockade experiments besides the already identified zeroes in Rydberg-Rydberg interactions for certain internal states [24] and atom pair alignments [25].…”

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confidence: 98%

Rabi Oscillations and Excitation Trapping in the Coherent Excitation of a Mesoscopic Frozen Rydberg Gas

et al. 2008

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We demonstrate the coherent excitation of a mesoscopic ensemble of about 100 ultracold atoms to Rydberg states by driving Rabi oscillations from the atomic ground state. We employ a dedicated beam shaping and optical pumping scheme to compensate for the small transition matrix element. We study the excitation in a weakly interacting regime and in the regime of strong interactions. When increasing the interaction strength by pair state resonances we observe an increased excitation rate through coupling to high angular momentum states. This effect is in contrast to the proposed and previously observed interaction-induced suppression of excitation, the so-called dipole blockade.PACS numbers: 03.65. Yz, 32.80.Pj, 32.80.Rm, 34.20.Cf, 34.60.+z Rydberg atoms, with their rich internal structure, have been in the focus of atomic physics for more than a century [1]. In the last decade Rydberg physics were extended to laser-cooled atomic gases which allowed the study of a frozen system with controllable, strong interactions and negligible thermal contributions. This has opened a wide field in both experiment and theory covering such diverse areas as resonant energy transfer [2,3], plasma formation [4,5], exotic molecules [6,7], and quantum random walks [8,9]. In addition, these frozen Rydberg systems have been proposed as a possible candidate for quantum information processing [10,11]. However, the coherent excitation of Rydberg atoms, an important prerequisite for quantum information protocols, has proven a challenging task. While Rabi oscillations between different Rydberg states have been demonstrated and thoroughly analyzed before [12], Rabi oscillations between the ground state and Rydberg states of atoms have not been observed directly so far, mainly owing to the small transition matrix element.In this Letter we report on the experimental realization and observation of Rabi oscillations between the ground and Rydberg states of ultracold atoms. We demonstrate how strong interatomic interactions influence the coherent excitation of a mesoscopic cloud of atoms. We show that an interaction-induced coupling to a larger number of internal states can be used to trap the excitation. Employed in a controlled way, this effect offers future applications in the experimental realization of quantum random walks with exciton trapping [9].Our experiments are performed with a magneto-optical trap (MOT) of about 10 7 87 Rb atoms at densities of 10 10 cm −3 and temperatures below 100 µK. Rydberg excitation is achieved with two counterpropagating laser beams at 780 nm and 480 nm (see Fig. 1). The laser at 780 nm is collimated to a waist of 1.1 mm ensuring a constant Rabi frequency of 2π × 55 MHz over the excitation volume as determined from Autler-Townes splittings [13]. The laser at 480 nm is referenced to a temperature stabilized Zerodur-resonator and its beam is shaped with a diffractive optical element that produces a flattop beam profile which is characterized with an adapted CCD camera with a spatial resolution of 5.6 µm. The m...

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Rabi Oscillations and Excitation Trapping in the Coherent Excitation of a Mesoscopic Frozen Rydberg Gas

et al. 2008

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“…In the absence of an external electric field, the Rydberg-Rydberg interactions are of the van der Waals type C 5 /R 5 or C 6 /R 6 . [39] In a static electric field, a Rydberg atom possesses a large permanent dipole moment p, which scales as ∼ qa 0 n 2 with q the electron charge, which leads to a much stronger and longer C 3 /R 3 interaction. A pair of Rydberg atoms i and j interact with each other via dipole-dipole potential V dd ,…”

Section: Rydberg State and Dipole Blockade Mechanismmentioning

confidence: 99%

“…However, for some angles V dd vanishes which is undesirable for dipole blockade purpose. [39] Fortunately, there is another method to induce a strong, isotropic interaction between Rydberg atoms, comparable to V dd . The resonant collisional process (Förster process) transfers energy between two atoms through the dipole-dipole interaction with strength ∼ ρ 1 ρ 2 /R 3 , where ρ 1 and ρ 2 are the dipole matrix elements between initial and final energy states of the interacting atoms.…”

Section: Rydberg State and Dipole Blockade Mechanismmentioning

confidence: 99%

“…For perfect Förster degeneracy (δ = 0) V + (R) would be of similar strength and range to V dd . [39] Although at the large separations, a non-zero Förster energy defect reduces long-range interaction between the atoms to be van der Waals C 6 /R 6 type. However, if the Förster energy defects are smaller compared to the fine-structure splitting, then strong C 3 /R 3 interaction can even occur at longer range.…”

Section: Rydberg State and Dipole Blockade Mechanismmentioning

confidence: 99%

“…Only for l = l = l + 1 there are no so-called Förster zero states with C 3 = 0. [39] Therefore, a fidelity of the dipole blockade mechanism is highly dependent on a weakest interactions between degenerate Rydberg states and may be reduced under unfortunate circumstances. In the case of the Förster zero states, strength of the interaction between Rydberg atoms is not enhanced and reduces to the usual van der Waals long-range type.…”

Section: Rydberg State and Dipole Blockade Mechanismmentioning

confidence: 99%

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Applications of Atomic Ensembles in Distributed Quantum Computing

Zwierz

Kok

2010

Int. J. Quantum Inform.

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Thesis chapter. The fragility of quantum information is a fundamental constraint faced by anyone trying to build a quantum computer. A truly useful and powerful quantum computer has to be a robust and scalable machine. In the case of many qubits which may interact with environment and their neighbors, protection against decoherence becomes quite a challenging task. The scalability and decoherence issues are the main difficulties addressed by the distributed model of quantum computation. A distributed quantum computer consists of a large quantum network of distant nodes -stationary qubits which communicate via flying qubits. Quantum information can be transferred, stored, processed and retrieved in decoherence-free fashion by nodes of a quantum network realized by an atomic mediuman atomic quantum memory. Atomic quantum memories have been developed and demonstrated experimentally in recent years. With a help of linear optics and laser pulses one is able to manipulate quantum information stored inside an atomic quantum memory by means of electromagnetically induced transparency and associated propagation phenomena. Any quantum computation or communication necessarily involves entanglement. Therefore, one must be able to entangle distant nodes of a distributed network. In this article, we focus on the probabilistic entanglement generation procedures such as well-known DLCZ protocol. We also demonstrate theoretically a scheme based on atomic ensembles and the dipole blockade mechanism for generation of inherently distributed quantum states so-called cluster states. In 1 the protocol, atomic ensembles serve as single qubit systems. Hence, we review single-qubit operations on qubit defined as collective states of atomic ensemble. Our entangling protocol requires nearly identical single-photon sources, one ultra-cold ensemble per physical qubit, and regular photodetectors. The general entangling procedure is presented, as well as a procedure that generates in a single step Q-qubit GHZ states with success probability p success ∼ η Q/2 , where η is the combined detection and source efficiency. This is significantly more efficient than any known robust probabilistic entangling operation. The GHZ states form the basic building block for universal cluster states, a resource for the one-way quantum computer.

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