arXiv subjects

M. D. Lukin

Publications and source records attributed to M. D. Lukin.

At least 127 records · Page 7Linked to original sources

arXiv2005

Engineering Superfluidity in Bose-Fermi Mixtures of Ultracold Atoms

We investigate many-body phase diagrams of atomic boson-fermion mixtures loaded in the two-dimensional optical lattice. Bosons mediate an attractive, finite-range interaction between fermions, leading to fermion pairing phases of different orbital symmetries. Specifically, we show that by properly tuning atomic and lattice parameters it is possible to create superfluids with $s$-, $p$-, and d-wave pairing symmetry as well as spin and charge density wave phases. These phases and their stability are analyzed within the mean-field approximation for systems of $^{40}$K-$^{87}$Rb and $^{40}$K-$^{23}$Na mixtures. For the experimentally accessible regime of parameters, superfluids with unconventional fermion pairing have transition temperature around a percent of the Fermi energy.

cond-mat.supr-con↗

arXiv2004

Nonlinear optics with stationary pulses of light

We show that the recently demonstrated technique for generating stationary pulses of light [Nature {\bf 426}, 638 (2003)] can be extended to localize optical pulses in all three spatial dimensions in a resonant atomic medium. This method can be used to dramatically enhance the nonlinear interaction between weak optical pulses. In particular, we show that an efficient Kerr-like interaction between two pulses can be implemented as a sequence of several purely linear optical processes. The resulting process may enable coherent interactions between single photon pulses.

quant-ph↗

arXiv2004

Quantum information processing using localized ensembles of nuclear spins

We describe a technique for quantum information processing based on localized en sembles of nuclear spins. A qubit is identified as the presence or absence of a collective excitation of a mesoscopic ensemble of nuclear spins surrounding a single quantum dot. All single and two-qubit operations can be effected using hyperfine interactions and single-electron spin rotations, hence the proposed scheme avoids gate errors arising from entanglement between spin and orbital degrees of freedom. Ultra-long coherence times of nuclear spins suggest that this scheme could be particularly well suited for applications where long lived memory is essential.

cond-mat.mes-hall↗

arXiv2004

Shaping quantum pulses of light via coherent atomic memory

We describe a technique for generating pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. The technique is based on preparation of an atomic ensemble in a state with a desired number of atomic spin excitations, which is later converted into a photon pulse. Spatio-temporal control over the pulses is obtained by exploiting long-lived coherent memory for photon states and electromagnetically induced transparency (EIT) in an optically dense atomic medium. Using photon counting experiments we observe generation and shaping of few-photon sub-Poissonian light pulses. We discuss prospects for controlled generation of high-purity n-photon Fock states using this technique.

quant-ph↗

arXiv2004

Luttinger liquid of polarons in one-dimensional boson-fermion mixtures

We use bosonization approach to investigate quantum phases in mixtures of bosonic and fermionic atoms confined in one dimensional optical lattices. The phase diagrams can be well understood in terms of polarons, which correspond to atoms that are "dressed" by screening clouds of the other atom species. For a mixture of single species of fermionic and bosonic atoms we find a charge density wave phase, a phase with fermion pairing, and a regime of phase separation. For a mixture of two species of fermionic atoms and one species of bosonic atoms we obtain spin and charge density wave phases, a Wigner crystal phase, singlet and triplet paired states of fermions, and a phase separation regime. Equivalence between the Luttinger liquid description of polarons and the canonical polaron transformation is established and the techniques to detect the resulting quantum phases are discussed.

quant-ph↗

arXiv2004

Stability of atomic clocks based on entangled atoms

We analyze the effect of realistic noise sources for an atomic clock consisting of a local oscillator that is actively locked to a spin-squeezed (entangled) ensemble of $N$ atoms. We show that the use of entangled states can lead to an improvement of the long-term stability of the clock when the measurement is limited by decoherence associated with instability of the local oscillator combined with fluctuations in the atomic ensemble's Bloch vector. Atomic states with a moderate degree of entanglement yield the maximal clock stability, resulting in an improvement that scales as $N^{1/6}$ compared to the atomic shot noise level.

quant-ph↗

arXiv2003

Stationary pulses of light in an atomic medium

Physical processes that could facilitate coherent control of light propagation are now actively explored. In addition to fundamental interest, these efforts are stimulated by possibilities to develop, for example, a quantum memory for photonic states. At the same time, controlled localization and storage of photonic pulses may allow novel approaches to manipulate light via enhanced nonlinear optical processes. Recently, Electromagnetically Induced Transparency (EIT) was used to reduce the group velocity of propagating light pulses and to reversibly map propagating light pulses into stationary spin excitations in atomic media. Here we describe and experimentally demonstrate a novel technique in which light propagating in a medium of Rb atoms is converted into an excitation with localized, stationary electromagnetic energy, which can be held and released after a controllable interval. Our method creates pulses of light with stationary envelopes bound to an atomic spin coherence, raising new possibilities for photon state manipulation and non-linear optical processes at low light levels.

quant-ph↗

arXiv2003

Controlling Spin Exchange Interactions of Ultracold Atoms in Optical Lattices

We describe a general technique that allows to induce and control strong interaction between spin states of neighboring atoms in an optical lattice. We show that the properties of spin exchange interactions, such as magnitude, sign, and anisotropy can be designed by adjusting the optical potentials. We illustrate how this technique can be used to efficiently ``engineer'' quantum spin systems with desired properties, for specific examples ranging from scalable quantum computation to probing a model with non-trivial topological orders that supports exotic non-abelian anyonic excitations.

cond-mat.soft↗

arXiv2003

Mesoscopic Cavity Quantum Electrodynamics with Quantum Dots

We describe an electrodynamic mechanism for coherent, quantum mechanical coupling between spacially separated quantum dots on a microchip. The technique is based on capacitive interactions between the electron charge and a superconducting transmission line resonator, and is closely related to atomic cavity quantum electrodynamics. We investigate several potential applications of this technique which have varying degrees of complexity. In particular, we demonstrate that this mechanism allows design and investigation of an on-chip double-dot microscopic maser. Moreover, the interaction may be extended to couple spatially separated electron spin states while only virtually populating fast-decaying superpositions of charge states. This represents an effective, controllable long-range interaction, which may facilitate implementation of quantum information processing with electron spin qubits and potentially allow coupling to other quantum systems such as atomic or superconducting qubits.

quant-ph↗

arXiv2003

Controlling a mesoscopic spin environment by quantum bit manipulation

We present a unified description of cooling and manipulation of a mesoscopic bath of nuclear spins via coupling to a single quantum system of electronic spin (quantum bit). We show that a bath cooled by the quantum bit rapidly saturates. Although the resulting saturated states of the spin bath (``dark states'') generally have low degrees of polarization and purity, their symmetry properties make them a valuable resource for the coherent manipulation of quantum bits. Specifically, we demonstrate that the dark states of nuclear ensembles can be used to coherently control the system-bath interaction and to provide a robust, long-lived quantum memory for qubit states.

cond-mat.mes-hall↗

arXiv2003

Controlling dipole-dipole frequency shifts in a lattice-based optical atomic clock

Motivated by the ideas of using cold alkaline earth atoms trapped in an optical lattice for realization of optical atomic clocks, we investigate theoretically the perturbative effects of atom-atom interactions on a clock transition frequency. These interactions are mediated by the dipole fields associated with the optically excited atoms. We predict resonance-like features in the frequency shifts when constructive interference among atomic dipoles occur. We theoretically demonstrate that by fine-tuning the coherent dipole-dipole couplings in appropriately designed lattice geometries, the undesirable frequency shifts can be greatly suppressed.

quant-ph↗

arXiv2003

Nonlinear optics via double dark resonances

Double dark resonances originate from a coherent perturbation of a system displaying electromagnetically induced transparency. We experimentally show and theoretically confirm that this leads to the possibility of extremely sharp resonances prevailing even in the presence of considerable Doppler broadening. A gas of 87Rb atoms is subjected to a strong drive laser and a weak probe laser and a radio frequency field, where the magnetic coupling between the Zeeman levels leads to nonlinear generation of a comb of sidebands.

quant-ph↗

arXiv2003

Long-lived memory for mesoscopic quantum bits

We describe a technique to create long-lived quantum memory for quantum bits in mesoscopic systems. Specifically we show that electronic spin coherence can be reversibly mapped onto the collective state of the surrounding nuclei. The coherent transfer can be efficient and fast and it can be used, when combined with standard resonance techniques, to reversibly store coherent superpositions on the time scale of seconds. This method can also allow for ``engineering'' entangled states of nuclear ensembles and efficiently manipulating the stored states. We investigate the feasibility of this method through a detailed analysis of the coherence properties of the system.

cond-mat.mes-hall↗

arXiv2002

High-temperature superfluidity of fermionic atoms in optical lattices

The experimental realizations of degenerate Bose and Fermi atomic samples have stimulated a new wave of studies of quantum many-body systems in the dilute and weakly interacting regime. The intriguing prospective of extending these studies into the domain of strongly correlated phenomena is hindered by the apparent relative weakness of atomic interactions. The effects due to interactions can, however, be enhanced if the atoms are confined in optical potentials created by standing light waves. The present letter shows that these techniques, when applied to ensembles of cold fermionic atoms, can be used to dramatically increase the transition temperature to a superfluid state and thus make it readily observable under current experimental conditions. Depending upon carefully controlled parameters, a transition to a superfluid state of Cooper pairs, antiferromagnetic states or more exotic d-wave pairing states can be induced and probed. The results of proposed experiments can provide a critical insight into the origin of high-temperature superconductivity in cuprates.

cond-mat.soft↗

arXiv2002

Manipulating Light Pulses via Dynamically Controlled Photonic Bandgap

When a resonance associated with electromagnetically induced transparency (EIT) in an atomic ensemble is modulated by an off-resonant standing light wave, a band of frequencies can appear for which light propagation is forbidden. We show that dynamic control of such a bandgap can be used to coherently convert a propagating light pulse into a stationary excitation with non-vanishing photonic component. This can be accomplished with high efficiency and negligble noise even at a level of few-photon quantum fields thereby facilitating possible applications in quantum nonlinear optics and quantum information.

quant-ph↗

arXiv2001

Coherent Atom Interactions Mediated by Dark-State Polaritons

We suggest a technique to induce effective, controllable interactions between atoms that is based on Raman scattering into an optical mode propagating with a slow group velocity. The resulting excitation corresponds to the creation of spin-flipped atomic pairs in a way that is analogous to correlated photon emission in optical parametric amplification. The technique can be used for fast generation of entangled atomic ensembles, spin squeezing and applications in quantum information processing.

quant-ph↗

arXiv2001

Atom correlations and spin squeezing near the Heisenberg limit: finite system size effect and decoherence

We analyze a model for spin squeezing based on the so-called counter-twisting Hamiltonian, including the effects of dissipation and finite system size. We discuss the conditions under which the Heisenberg limit, i.e. phase sensitivity $\propto 1/N$, can be achieved. A specific implementation of this model based on atom-atom interactions via quantized photon exchange is presented in detail. The resulting excitation corresponds to the creation of spin-flipped atomic pairs and can be used for fast generation of entangled atomic ensembles, spin squeezing and apllications in quantum information processing. The conditions for achieving strong spin squeezing with this mechanism are also analyzed.

quant-ph↗

arXiv2001

Mesoscopic molecular ions in Bose-Einstein condensates

We study the possible formation of large (mesoscopic) molecular ions in an ultracold degenerate bosonic gas doped with charged particles (ions). We show that the polarization potentials produced by the ionic impurities are capable of capturing hundreds of atoms into loosely bound states. We describe the spontaneous formation of these hollow molecular ions via phonon emission and suggest an optical technique for coherent stimulated transitions of free atoms into a specific bound state. These results open up new interesting possibilities for manipulating tightly confined ensembles.

quant-ph↗