Generating and Probing a Two-Photon Fock State with a Single Atom in a Cavity (original) (raw)
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Cavity-Based Single Atom Preparation and High-Fidelity Hyperfine State Readout
Physical Review Letters, 2010
We prepare and detect the hyperfine state of a single 87 Rb atom coupled to a fiber-based high finesse cavity on an atom chip. The atom is extracted from a Bose-Einstein condensate and trapped at the maximum of the cavity field, resulting in a reproducibly strong atom-cavity coupling. We use the cavity reflection and transmission signal to infer the atomic hyperfine state with a fidelity exceeding 99.92% in a read-out time of 100 µs. The atom is still trapped after detection. PACS numbers: 42.50.Pq, 42.50.Dv, 67.85.Hj A single neutral atom with two hyperfine ground states provides a long-lived two-level system ideally suited for quantum information purposes. The collisional interaction between two atoms in the vibrational ground state is a powerful mechanism for the creation of entanglement in this system [1, 2]. This has been demonstrated for atoms in the Mott insulator state in an optical lattice loaded from a Bose-Einstein condensate (BEC) . However, single-site addressability is challenging in these experiments . Bottom-up approaches starting with lasercooled single atoms in easily addressable macroscopic traps [6-9] and on atom chips have not yet succeeded in ground state preparation. Furthermore, read-out of the qubit state is usually destructive and does not fulfill the requirements for efficient quantum error correction .
Controlled generation of single photons from a strongly coupled atom-cavity system
Applied Physics B, 1999
We propose a new method for the generation of single photons. Our scheme will lead to the emission of one photon into a single mode of the radiation field in response to a trigger event. This photon is emitted from an atom strongly coupled to a high-finesse optical cavity, and the trigger is a classical light pulse. The device combines cavity-QED with an adiabatic transfer technique. We simulate this process numerically and show that it is possible to control the temporal behaviour of the photon emission probability by the shape and the detuning of the trigger pulse. An extension of the scheme with a reloading mechanism will allow one to emit a bit-stream of photons at a given rate.
Classical Behavior with Small Quantum Numbers: The Physics of Ramsey Interferometry of Rydberg Atoms
In Ramsey atomic interferometry, a superposition of atomic states is produced by a mechanism completely equivalent (for experimental purposes) to interaction with a classical field. Since this property holds, in the case of Rydberg atoms, for temperatures close to absolute zero and field intensities of the order of a single photon, the question arises as to why the quantum nature of the field can be neglected. We model the passage of an atom through a Ramsey zone and show that, in order to explain the phenomenon, correlation properties between three subsystems and strong cavity dissipation turn out to be the essential physical ingredients leading to classical behavior. [S0031-9007(99)09302-3] PACS numbers: 39.20. + q, 42.50.Lc Microwave cavities are extensively used in experiments designed to access fundamental issues concerning the interaction of atoms and electromagnetic field modes in the context of cavity quantum electrodynamics [1]. In Ramsey atomic interferometry [2], in particular, they are known to generate quantum superpositions of atomic states as if the field inside them were of a classical nature. Two cavities separated by an intermediate region are filled with fields oscillating with phase coherence so that atomic transition probability amplitudes undergo quantum superpositions observed as interference (Ramsey) fringes. When this situation holds for temperatures close to absolute zero and field intensities of the order of a single photon, one may ask to what extent the quantum nature of the field can be neglected and how can this be theoretically modeled from basic quantum theory.
Trapping and photon number states in a two-photon micromaser
Journal of Luminescence, 1998
We present a theoretical analysis of a two-photon micromaser and investigate the statistical properties of the radiation. We analyze both vacuum as well as non-vacuum trapped states that follow from the theory. Non-vaccum trapped states have not been found in previous theories of the two-photon micromaser. We explore how photon number states can be generated in the limit of large flux of atoms in the cavity.
Single photon transfer controlled by excitation phase in a two-atom cavity system
Journal of Physics B: Atomic, Molecular and Optical Physics
We investigate the quantum interference effects of single photon transfer in two-atom cavity system caused by external excitation phase. In the proposed system, two identical atoms (with different positions in the optical cavity) are firstly prepared into a timed state by an external single photon field. During the excitation, the atoms grasp different phases which depend on the spatial positions of the atoms in the cavity. Due to strong resonant interaction between two atoms and optical cavity mode the absorbed input photon can be efficiently transferred from the atoms to the resonant cavity mode. We show that the quantum transfer is highly sensitive to the external excitation phases of atoms and it leads to quantum interference effects on the cavity mode excitation. Besides, the quantum transfer is also influenced by the dipole-dipole interaction dependent to the atomic distance. In this system the atomic positions also determine the coupling constants between atoms and cavity mode which causes additional interference effects to the photon exchange between atoms and cavity. Based on the characteristics of excitation phase we find that it is a feasible scheme to generate long-lived dark state and it could be useful for storage and manipulation of single photon fields by controlling the excitation phase.
Journal of Experimental and Theoretical Physics, 2018
We study the evolution of entanglement for a pair of two-level Rydberg atoms passing one after another into an ideal cavity filled with a single mode radiation field. The atoms interact with the cavity field via two-photon transitions. The initial joint state of two atoms that enter the cavity one after the other is unentangled. Interactions intervened by the single mode cavity photon field brings out the final two-atom mixed entangled type state. We use the well known measure appropriate for the mixed states, i.e. the entanglement of formation to quantify the entanglement. We calculate the entanglement of formation of the joint two-atom state as a function of the Rabi angle, for the Fock state field, coherent field and thermal field respectively inside the cavity. The change in the magnitude of atomic entanglement with cavity photon number has been discussed.
A single-photon server with just one atom
Nature Physics, 2007
Neutral atoms are ideal objects for the deterministic processing of quantum information. Entanglement operations have been carried out by photon exchange 1 or controlled collisions 2 , and atom-photon interfaces have been realized with single atoms in free space 3,4 or strongly coupled to an optical cavity 5,6. A long-standing challenge with neutral atoms, however, is to overcome the limited observation time. Without exception, quantum effects appeared only after ensemble averaging. Here, we report on a single-photon source with one, and only one, atom quasi-permanently coupled to a high-finesse cavity. 'Quasipermanent' refers to our ability to keep the atom long enough to, first, quantify the photon-emission statistics and, second, guarantee the subsequent performance as a single-photon server delivering up to 300,000 photons for up to 30 s. This is achieved by a unique combination of single-photon generation and atom cooling 7-9. Our scheme brings deterministic protocols of quantum information science with light and matter 10-16 closer to realization. Deterministic single-photon sources are of prime importance in quantum information science 17. Such sources have been realized with neutral atoms, embedded molecules, trapped ions, quantum dots and defect centres 18. All of these sources are suitable for applications where the indivisibility of the emitted light pulses is essential. For quantum computing or quantum networking, the emitted photons must also be indistinguishable. Such photons have so far only been produced with quantum dots 19 and atoms 20,21. Another requirement is a high efficiency. This is hard to obtain in free space, as the light-collecting lens covers only a fraction of the full 4π solid angle. The efficiency can be boosted by strongly coupling the radiating object to an optical microcavity, as has been achieved with atoms 5,6 and quantum dots 22. An additional advantage of the cavity is that a vacuum-stimulated Raman adiabatic passage can be driven in a multilevel atom 6,23,24. In this way, the amplitude 5,24 , frequency 20 and polarization 25 of the photon can be controlled. It should also be possible to combine partial photon production with internal atomic rotations for the construction of entangled photon states such as W and GHZ states 15. All of these demands together have so far only been achieved with atoms in high-finesse microcavities. One reason is that neutral atoms are largely immune to perturbations, such as electric patch fields close to dielectric mirrors. However, atomic systems have always suffered from a fast atom loss. We have now implemented a cavity-based scheme, see Fig. 1, with a dipole laser for trapping, a trigger laser for photon generation and a recycling laser for Beam splitter Detector 1 Trigger and recycling laser Rb atom Cavity Dipole trap Detector 2
Optical qubit generation via atomic postselection in a Ramsey interferometer
Physica Scripta, 2018
We propose a realizable experimental scheme to prepare a superposition of the vacuum and one-photon states using a typical cavity QED-setup. This is different from previous schemes, where the superposition state of the field is generated by resonant atom-field interaction and the cavity is initially empty. Here, we consider only dispersive atom-field interaction and the initial state of the cavity field is coherent. Then, we determine the parameters to prepare the desired state via atomic postselection. We also include the effect of cavity losses and detection imperfections in our analysis, against which this preparation of the optical qubit in a real Fabry-Pérot superconducting cavity is robust. Additionally, we show that this scheme can be used for the preparation of other photon number Fock state superpositions. In summary, our task is achieved with a high fidelity and a postselection probability within experimental reach
Quantum interference and atom-atom entanglement in a two-mode, two-cavity micromaser
Physical Review A, 1999
The interaction of two-level atoms with two modes of a resonator, formed by two weakly coupled cavities, is investigated. The first atom, passing through one of the two cavities, excites the two field modes. The second atom then, passing through the other cavity, tests the excitation. Since the photon generated by the first atom may be in the first or the second cavity, quantum interference phenomena are observed. Furthermore, the setup can be used to generate maximum entangled pairs of atoms. ͓S1050-2947͑99͒08709-0͔