32 research outputs found
Probing quantum phases of ultracold atoms in optical lattices by transmission spectra in cavity QED
Studies of ultracold atoms in optical lattices link various disciplines,
providing a playground where fundamental quantum many-body concepts, formulated
in condensed-matter physics, can be tested in much better controllable atomic
systems, e.g., strongly correlated phases, quantum information processing.
Standard methods to measure quantum properties of Bose-Einstein condensates
(BECs) are based on matter-wave interference between atoms released from traps
which destroys the system. Here we propose a nondestructive method based on
optical measurements, and prove that atomic statistics can be mapped on
transmission spectra of a high-Q cavity. This can be extremely useful for
studying phase transitions between Mott insulator and superfluid states, since
various phases show qualitatively distinct light scattering. Joining the
paradigms of cavity quantum electrodynamics (QED) and ultracold gases will
enable conceptually new investigations of both light and matter at ultimate
quantum levels, which only recently became experimentally possible. Here we
predict effects accessible in such novel setups.Comment: 6 pages, 3 figure
Cavity QED with a Bose-Einstein condensate
Cavity quantum electrodynamics (cavity QED) describes the coherent
interaction between matter and an electromagnetic field confined within a
resonator structure, and is providing a useful platform for developing concepts
in quantum information processing. By using high-quality resonators, a strong
coupling regime can be reached experimentally in which atoms coherently
exchange a photon with a single light-field mode many times before dissipation
sets in. This has led to fundamental studies with both microwave and optical
resonators. To meet the challenges posed by quantum state engineering and
quantum information processing, recent experiments have focused on laser
cooling and trapping of atoms inside an optical cavity. However, the tremendous
degree of control over atomic gases achieved with Bose-Einstein condensation
has so far not been used for cavity QED. Here we achieve the strong coupling of
a Bose-Einstein condensate to the quantized field of an ultrahigh-finesse
optical cavity and present a measurement of its eigenenergy spectrum. This is a
conceptually new regime of cavity QED, in which all atoms occupy a single mode
of a matter-wave field and couple identically to the light field, sharing a
single excitation. This opens possibilities ranging from quantum communication
to a wealth of new phenomena that can be expected in the many-body physics of
quantum gases with cavity-mediated interactions.Comment: 6 pages, 4 figures; version accepted for publication in Nature;
updated Fig. 4; changed atom numbers due to new calibratio
Quantum Non-Demolition Detection of Strongly Correlated Systems
Preparation, manipulation, and detection of strongly correlated states of
quantum many body systems are among the most important goals and challenges of
modern physics. Ultracold atoms offer an unprecedented playground for
realization of these goals. Here we show how strongly correlated states of
ultracold atoms can be detected in a quantum non-demolition scheme, that is, in
the fundamentally least destructive way permitted by quantum mechanics. In our
method, spatially resolved components of atomic spins couple to quantum
polarization degrees of freedom of light. In this way quantum correlations of
matter are faithfully mapped on those of light; the latter can then be
efficiently measured using homodyne detection. We illustrate the power of such
spatially resolved quantum noise limited polarization measurement by applying
it to detect various standard and "exotic" types of antiferromagnetic order in
lattice systems and by indicating the feasibility of detection of superfluid
order in Fermi liquids.Comment: Published versio
Merging quantum optics and quantum many-body atomic systems
A system joining the problems of quantum optics and quantum gases - ultracold atoms trapped in an optical lattice inside a cavity - is considered. Thus, the quantum natures of both the light and atomic motion play equally important roles in the process [1-4]. This is in striking contrast to the majority of theoretical and experimental problems on ultracold gases, where the role of light is reduced to a classical auxiliary tool for trapping and manipulating intriguing atomic states. © 2011 IEEE
Merging quantum optics and quantum many-body atomic systems
A system joining the problems of quantum optics and quantum gases - ultracold atoms trapped in an optical lattice inside a cavity - is considered. Thus, the quantum natures of both the light and atomic motion play equally important roles in the process [1-4]. This is in striking contrast to the majority of theoretical and experimental problems on ultracold gases, where the role of light is reduced to a classical auxiliary tool for trapping and manipulating intriguing atomic states. © 2011 IEEE
Quantum optical measurements in ultracold gases: macroscopic Bose-Einstein condensates
We consider an ultracold quantum degenerate gas in an optical lattice inside a cavity. This system represents a simple but key model for "quantum optics with quantum gases," where a quantum description of both light and atomic motion is equally important. Due to the dynamical entanglement of atomic motion and light, the measurement of light affects the many-body atomic state as well. The conditional atomic dynamics can be described using the Quantum Monte Carlo Wave Function Simulation method. In this paper, we emphasize how this usually complicated numerical procedure can be reduced to an analytical solution after some assumptions and approximations valid for macroscopic Bose-Einstein condensates (BEC) with large atom numbers. The theory can be applied for lattices with both low filling factors (e.g. one atom per lattice site in average) and very high filling factors (e.g. a BEC in a double-well potential). The purity of the resulting multipartite entangled atomic state is analyzed
Engineering many-body dynamics with quantum light potentials and measurements
Interactions between many-body atomic systems in optical lattices and light in cavities induce long-range and correlated atomic dynamics beyond the standard Bose-Hubbard model, due to the global nature of the light modes. We characterize these processes, and show that uniting such phenomena with dynamical constraints enforced by the backaction resultant from strong light measurement leads to a synergy that enables the atomic dynamics to be tailored, based on the particular optical geometry, exploiting the additional structure imparted by the quantum light field. This leads to a range of tunable effects such as long-range density-density interactions, perfectly correlated atomic tunneling, superexchange, and effective pair processes. We further show that this provides a framework for enhancing quantum simulations to include such long-range and correlated processes, including reservoir models and dynamical global gauge fields
Quantum optics with quantum gases: controlled state reduction by designed light scattering
Cavity enhanced light scattering off an ultracold gas in an optical lattice constitutes a quantum measurement with a controllable form of the measurement back-action. Time-resolved counting of scattered photons alters the state of the atoms without particle loss implementing a quantum nondemolition (QND) measurement. The conditional dynamics is given by the interplay between photodetection events (quantum jumps) and no-count processes. The class of emerging atomic many-body states can be chosen via the optical geometry and light frequencies. Light detection along the angle of a diffraction maximum (Bragg angle) creates an atom-number squeezed state, while light detection at diffraction minima leads to the macroscopic superposition states (Schroedinger cat states) of different atom numbers in the cavity mode. A measurement of the cavity transmission intensity can lead to atom-number squeezed or macroscopic superposition states depending on its outcome. We analyze the robustness of the superposition with respect to missed counts and find that a transmission measurement yields more robust and controllable superposition states than the ones obtained by scattering at a diffraction minimum
Bond order via light-induced synthetic many-body interactions of ultracold atoms in optical lattices
We show how bond order emerges due to light mediated synthetic interactions in ultracold atoms in optical lattices in an optical cavity. This is a consequence of the competition between both short- and long-range interactions designed by choosing the optical geometry. Light induces effective many-body interactions that modify the landscape of quantum phases supported by the typical Bose–Hubbard model. Using exact diagonalization of small system sizes in one-dimension, we present the many-body quantum phases the system can support via the interplay between the density and bond (or matter–wave coherence) interactions. We find numerical evidence to support that dimer phases due to bond order are analogous to valence bond states. Different possibilities of light-induced atomic interactions are considered that go beyond the typical atomic system with dipolar and other intrinsic interactions. This will broaden the Hamiltonian toolbox available for quantum simulation of condensed matter physics via atomic systems