Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G33: Quantum Entanglement I |
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Sponsoring Units: GQI Chair: Josh Combes, University of New Mexico Room: 706 |
Tuesday, March 4, 2014 11:15AM - 11:27AM |
G33.00001: Universal entanglement crossover of coupled quantum wires Romain Vasseur, Jesper Jacobsen, Hubert Saleur We consider the entanglement between two one-dimensional quantum wires (Luttinger Liquids) coupled by tunneling through a quantum impurity. The physics of the system involves a crossover between weak and strong coupling regimes characterized by an energy scale $T_B$, and methods of conformal field theory therefore cannot be applied. The evolution of the entanglement in this crossover has led to many numerical studies, but has remained little understood, analytically or even qualitatively. This is, in part, due to the fact that the entanglement in this case is non-perturbative in the tunneling amplitude. We argue that the correct universal scaling form of the entanglement entropy $S$ (for an arbitrary interval containing the impurity) is $\partial S/\partial \ln L = f(L T_B)$. In the special case where the coupling to the impurity can be refermionized, we show how the universal function $f(L T_B)$ can be obtained analytically using recent results on form factors of twist fields and a defect massless-scattering formalism. Our results are carefully checked against numerical simulations. [Preview Abstract] |
Tuesday, March 4, 2014 11:27AM - 11:39AM |
G33.00002: Rapid creation of distant entanglement by multi-photon resonant fluorescence Guy Z. Cohen, L.J. Sham We study a simple, effective and robust method for entangling two separate stationary quantum dot spin qubits with high fidelity using multi-photon Gaussian state. The fluorescence signals from the two dots interfere at a beam splitter. The bosonic nature of photons leads, in analogy with the Hong-Ou-Mandel (HOM) effect, to selective pairing of photon holes (photon absences in the fluorescent signals). By the HOM effect, two photon holes with the same polarization end up at the same beam splitter output. As a result, two odd photon number detections at the outgoing beams, which must correspond to two photon holes with different polarizations, herald entanglement creation. The robustness of the Gaussian states is evidenced by the ability to compensate for photon absorption and noise by a moderate increase in the number of photons at the input. We calculate the entanglement generation rate in the ideal, non-ideal and near-ideal detector regimes and find substantial improvement over single-photon schemes in all three regimes. Fast and efficient spin-spin entanglement creation can form the basis for a scalable quantum dot quantum computing network. Our predictions can be tested using current experimental capabilities. [Preview Abstract] |
Tuesday, March 4, 2014 11:39AM - 11:51AM |
G33.00003: From remote entanglement between solid state qubits to deterministic quantum teleportation Hannes Bernien, Bas Hensen, Wolfgang Pfaff, Gerwin Koolstra, Suzanne van Dam, Machiel Blok, Lucio Robledo, Tim Taminiau, Matthew Markham, Daniel Twitchen, Lilian Childress, Ronald Hanson Quantum networks enable the distribution of quantum information that is processed and stored in local nodes [1]. Setting up a quantum network requires the generation of entanglement between widely separated qubits combined with local long-lived quantum registers. Here we present our recent results towards the realization of scalable quantum networks with solid-state qubits. We have entangled two spin qubits, each associated with a nitrogen vacancy center in diamond [2]. The two diamonds reside in separate setups three meters apart from each other. With no direct interaction between the two spins to mediate the entanglement, we make use of a scheme based on quantum measurements: we perform a joint measurement on photons emitted by the NV centers. The detection of the photons projects the spins into an entangled state. We verify the generated entanglement by single-shot readout of the spin qubits in different bases and correlating the results. We will present these experiments along with our latest results towards deterministic quantum teleportation between distant qubits. [1] H. J. Kimble, Nature, 453, 1023 (2008) [2] H. Bernien et al., Nature 497, 86 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G33.00004: Shadow Lattice Stabilization Program for Strongly Correlated States of Light Eliot Kapit, Mohammad Hafezi, Steven Simon Recent progress in nanoscale quantum optics and superconducting qubits has made the creation and quantum simulation of strongly correlated, and even topologically ordered, states of photons a real possibility. Many of these states are gapped and exhibit anyon excitations, which could be used for quantum information processing. However, the question of how to stabilize the many-body ground states of photonic quantum simulators against decays remains largely unanswered. We here propose a simple mechanism which achieves this goal. Our construction uses a uniform two-photon drive field to entangle the qubits of the primary lattice with an auxiliary ``shadow" lattice of qubits with a much faster loss rate than the primary qubits. This entanglement raidly refills hole states created by photon losses, and a many-body gap prevents further photons from being added once the strongly correlated ground state is reached. We present a set of general guidelines for designing the shadow lattice and coupling Hamiltonians to stabilize the ground state of a given primary Hamiltonian. We then provide an explicit construction which stabilizes abelian and non-abelian fractional quantum Hall states of light. The device parameters needed for our scheme to work are within reach of current technology. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G33.00005: Demonstration of Quantum Entanglement in an Analog Electronic Device Brian La Cour, Granville Ott, Gary Wilson, Marti Barlett There are a surprising number of classical analogs to phenomena generally regarded as uniquely quantum in nature. We consider one such analog that uses complex basebanded signals in a classical electronic device to represent a multi-qubit quantum state. Formally, such a representation is capable of reproducing the mathematical structure of a tensor-product Hilbert space. In particular, entangled bipartite states can be represented in this manner. As a demonstration of this concept, we describe an experiment using an analog electronic device capable of emulating an arbitrary two-qubit system. We then show how, using a pair of independent ``Alice'' and ``Bob'' analog measurement devices, one can achieve correlations in violation of Bell's inequality, much as those found in optical tests of quantum nonlocality. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G33.00006: Experimental distribution of entanglement with separable carriers Alessandro Fedrizzi, Margherita Zuppardo, Geoff Gillett, Matthew Broome, Marcelo de Almeida, Mauro Paternostro, Andrew White, Tomasz Paterek Quantum networks will allow us to overcome distance limitations in quantum communication, and to share quantum computing tasks between remote quantum processors. The key requirement for quantum networking is the distribution of entanglement between nodes. Surprisingly, entanglement can be generated across a network without directly being communicated between nodes. In contrast to information gain, which cannot exceed the communicated information, the entanglement gain is bounded by the communicated quantum discord, a more general measure of quantum correlation that includes but is not limited to entanglement. Here we report an experiment in which two communicating parties who share three initially separable photonic qubits are entangled by exchange of a carrier photon that is not entangled with either party at all times. We show that distributing entanglement with separable carriers is resilient to noise and in some cases becomes the only way of distributing entanglement over noisy environments. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G33.00007: Entanglement of formation in the Kondo model at finite temperature Seung-Sup Lee, Jinhong Park, H.-S. Sim We compute the entanglement of formation, a generalization of the entanglement entropy quantifying any bipartite entanglement in mixed states, in the Kondo model at finite temperature $T$, using a new approach [1,2] based on the optimal entanglement witness operator and the numerical renormalization group method. We focus on the entanglement between the Kondo impurity spin and the electrons lying inside distance $L$ from the impurity. The entanglement characterizes the thermal suppression and the spatial profile of the macroscopic quantum correlations in the Kondo systems, providing the quantum information perspective of the Kondo cloud. We reveal the universal scaling behaviors of the entanglement at low $T$ and large $L$. [1] S.-S. B. Lee and H.-S. Sim, Phys. Rev. A \textbf{85}, 022325 (2012). [2] S. Ryu, S.-S. B. Lee, and H.-S. Sim, Phys. Rev. A \textbf{86}, 042324 (2012). [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G33.00008: Generation of Massive Entanglement Through Adiabatic Quantum Phase Transition in a spinor condensate Zhen Zhang, Luming Duan We propose a method to generate massive entanglement in a spinor Bose-Einstein condensate from an initial product state through adiabatic sweep of magnetic field across a quantum phase transition induced by competition between the spin-dependent collision interaction and the quadratic Zeeman effect. The generated many-body entanglement is characterized by the experimentally measurable entanglement depth in the proximity of the Dicke state. We show that the scheme is robust to practical noise and experimental imperfection and under realistic conditions it is possible to generate genuine entanglement for hundreds of atoms. [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G33.00009: Deterministic generation of many-photon GHZ states using quantum dots in a cavity Michael Leuenberger, Mikhail Erementchouk, Ahmed Elhalawany We propose a novel theoretical scheme based on the off-resonant interaction of $N$ photons with four InAs/GaAs semiconductor quantum dots (QDs) in an GaAs microdisk cavity to create many-photon GHZ states deterministically in the polarization degree of freedom at a wavelength of 1.3 $\mu$m with probability $p=1$ for $N$ up to 60, without the need of any projective measurement or local unitary operation. Taking advantage of off-resonant interaction, the time evolution of the $N$-photon state is robust against decoherence due to exciton-phonon and hyperfine interactions. However, decoherence due to leakage of the photons out of the cavity is not negligible and is therefore considered. Remarkably, by taking advantage of a cascaded multi-level Landau-Zener transition, we are able to reduce the GHZ state generation time to below 100 ps for $N$ up to 60, which allows for the creation of GHZ states with $N$ up to 60 in cavities with $Q=10^6$ with fidelity above 70\% including decoherence due to leakage. Our method paves the way to the miniaturization of many-photon GHZ state sources to the nanoscale regime, with the possibility to integrate them on a computer chip based on semiconductor materials. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G33.00010: Entanglement Generation in a Two-Qubit System Coupled to Vacuum Electromagnetic Field Saeed Pegahan The entanglement generation in a two-qubit system interacting with electromagnetic vacuum field and an external local magnetic field is investigated in the framework of the master equation. The time-evolution for the most general density matrix of the two-qubit system is obtained and solved. It is shown that the two-qubit system ends up in an entangled stationary state independent on the initial separable state. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G33.00011: Many-body localization: Local integrals of motion, area-law entanglement, and quantum dynamics Dmitry Abanin, Maksym Serbyn, Zlatko Papic We demonstrate that the many-body localized phase is characterized by the existence of infinitely many local conservation laws. We argue that many-body eigenstates can be obtained from product states by a sequence of nearly local unitary transformation, and therefore have an area-law entanglement entropy, typical of ground states. Using this property, we construct the local integrals of motion in terms of projectors onto certain linear combinations of eigenstates. The local integrals of motion can be viewed as effective quantum bits which have a conserved z-component that cannot decay. Thus, the dynamics is reduced to slow dephasing between distant effective bits. For initial product states, this leads to a characteristic slow power-law decay of local observables, which is measurable experimentally, as well as to logarithmic in time growth of entanglement entropy. We support our findings by numerical simulations of random-field XXZ spin chains. Our work shows that the many-body localized phase is integrable, reveals a simple entanglement structure of eigenstates, and establishes the laws of dynamics in this phase. [1] M. Serbyn, Z. Papic, D. A. Abanin, Phys. Rev. Lett. 111, 127201 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G33.00012: Entanglement propagation and typicality of measurements in a quantum version of the Kac ring Johannes Oberreuter, Ingo Homrighausen, Stefan Kehrein Time development in quantum many body systems poses serious challenges to our understanding of classical statistical mechanics. Exact results are very rare due to the large Hilbert spaces and the resulting complexity involved. We propose a pedagogical approach with a very tractable toy model, in which questions of entanglement creation, propagation and destruction between a system and an environment can be studied explicitly. Comparing this quantum model with its classical counterpart [1], we find an intriguing correspondence between the typical result of repeated measurements on a classical ensemble and the repeated measurements of a quantum system in an appropriate superposition. \\[4pt] [1] G.A. Gottwald, M. Oliver, Boltzmann's Dilemma: An Introduction to Statistical Mechanics via the Kac Ring, SIAM Review (2009) Vol. 51, No. 3, pp. 613-635. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G33.00013: Universal slow growth of entanglement in interacting strongly disordered systems Maksym Serbyn, Zlatko Papic, Dmitry Abanin Localized phase of interacting particles has recently been shown to have a slow, logarithmic in time, growth of the entanglement entropy for initial product states. This property has been conjectured to distinguish the many-body localized phase from the ordinary Anderson insulator. In the present work we put this assumption on solid ground by uncovering the underlying mechanism of the entanglement generation. We show that the entanglement arises from dephasing due to exponentially small interaction-induced corrections to the eigenenergies of different states. For weak interactions, we find that the entanglement entropy grows as $\xi \ln (Vt/\hbar)$ with time $t$, where $V$ is the interaction strength and $\xi$ is the single-particle localization length. The saturated value of the entanglement entropy at long times is determined by the participation ratios of the initial state over the eigenstates of the subsystem. Our work shows that the logarithmic entanglement growth is a universal phenomenon characteristic of the many-body localized phase in any number of spatial dimensions, and reveals a broad hierarchy of dephasing time scales present in such a phase. [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G33.00014: Violation of the Entanglement Area Law in Bosonic Systems with Bose Surfaces: Possible Application to Bose Metals Hsin-Hua Lai, Kun Yang, Nicholas Bonesteel We show the violation of the entanglement-area law for bosonic systems with Bose surfaces. For bosonic systems with gapless factorized energy dispersions on a $N^d$ Cartesian lattice in $d$-dimension, e.g., the exciton Bose liquid in two dimension, we explicitly show that a belt subsystem with width $L$ preserving translational symmetry along $d-1$ Cartesian axes has leading entanglement entropy $(N^{d-1}/3)\ln L$. Using this result, the strong subadditivity inequality, and lattice symmetries, we bound the entanglement entropy of a rectangular subsystem from below and above showing a logarithmic violation of the area law. For subsystems with a single flat boundary we also bound the entanglement entropy from below showing a logarithmic violation, and argue that the entanglement entropy of subsystems with arbitrary smooth boundaries are similarly bounded. [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G33.00015: Environmental Entanglement Caused by a Qubit: Multipolaron Ansatz for Biased Spin-Boson Model Soumya Bera, S. Florens, H. Baranger, A. Nazir, A. Chin We show that a qubit interacting with its environment produces highly entangled states within the environment with emerging non-adiabatic features (Schrodinger-cat-like states of the environment). The model consists of a two-level system coupled to a continuum of bath modes in the presence of a bias field, which can be realized, for instance, by a qubit coupled to a high impedance superconducting transmission line. We develop a systematic coherent state expansion for the many-body ground state of this model. Comparisons to accurate numerical renormalization group calculations and the exact Bethe Ansatz solution of the model demonstrate the rapid convergence of our variationally-optimized multi-polaron expansion. This coherent state Ansatz captures all the essential features of the biased model such as the formation of low-energy antipolarons, peaks seen in the quantum tomography of the environment, and the stabilization of spin coherence. [Preview Abstract] |
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