Recursos de colección
Caltech Authors (147.820 recursos)
Repository of works by Caltech published authors.
Group = IQIM
Repository of works by Caltech published authors.
Group = IQIM
Mross, David F.; Alicea, Jason; Motrunich, Olexei I.
Recent work on a family of boson-fermion mappings has emphasized the
interplay of symmetry and duality: Phases related by a particle-vortex duality
of bosons (fermions) are related by time-reversal symmetry in their fermionic
(bosonic) formulation. We present exact mappings for a number of concrete
models that make this property explicit on the operator level. We illustrate
the approach with one- and two-dimensional quantum Ising models, and then
similarly explore the duality web of complex bosons and Dirac fermions in (2+1)
dimensions.
Raussendorf, Robert; Browne, Dan E.; Delfosse, Nicolas; Okay, Cihan; Bermejo-Vega, Juan
We describe schemes of quantum computation with magic states on qubits for which contextuality and negativity of the Wigner function are necessary resources possessed by the magic states. These schemes satisfy a constraint. Namely, the non-negativity of Wigner functions must be preserved under all available measurement operations. Furthermore, we identify stringent consistency conditions on such computational schemes, revealing the general structure by which negativity of Wigner functions, hardness of classical simulation of the computation, and contextuality are connected.
Ma, Yiqiu; Miao, Haixing; Pang, Belinda Heyun; Evans, Matthew; Zhao, Chunnong; Harms, Jan; Schnabel, Roman; Chen, Yanbei
In continuously monitored systems the standard quantum limit is given by the trade-off between shot noise and back-action noise. In gravitational-wave detectors, such as Advanced LIGO, both contributions can be simultaneously squeezed in a broad frequency band by injecting a spectrum of squeezed vacuum states with a frequency-dependent squeeze angle. This approach requires setting up an additional long baseline, low-loss filter cavity in a vacuum system at the detector’s site. Here, we show that the need for such a filter cavity can be eliminated, by exploiting Einstein–Podolsky–Rosen (EPR)-entangled signals and idler beams. By harnessing their mutual quantum correlations and the...
Shi, T.; Kimble, H. J.; Cirac, J. I.
We propose a scheme to realize a topological insulator with optical-passive
elements, and analyze the effects of Kerr-nonlinearities in its topological
behavior. In the linear regime, our design gives rise to an optical spectrum
with topological features and where the bandwidths and bandgaps are
dramatically broadened. The resulting edge modes cover a very wide frequency
range. We relate this behavior to the fact that the effective Hamiltonian
describing the system's amplitudes is long-range. We also develop a method to
analyze the scheme in the presence of a Kerr medium. We assess robustness and
stability of the topological features, and predict the presence of chiral
squeezed fluctuations at the edges...
González-Tudela, A.; Paulisch, V.; Kimble, H. J.; Cirac, J. I.
In spite of decades of effort, it has not yet been possible to create
single-mode multiphoton states of light with high success probability and near
unity fidelity. Complex quantum states of propagating optical photons would be
an enabling resource for diverse protocols in quantum information science,
including for interconnecting quantum nodes in quantum networks. Here, we
propose several methods to generate heralded mutipartite entangled atomic and
photonic states by using the strong and long-range dissipative couplings
between atoms emerging in waveguide QED setups. Our theoretical analysis
demonstrates high success probabilities and fidelities are possible exploiting
waveguide QED properties.
Asenjo-Garcia, A.; Moreno-Cardoner, M.; Albrecht, A.; Kimble, H. J.; Chang, D. E.
A central goal within quantum optics is to realize efficient interactions
between photons and atoms. A fundamental limit in nearly all applications based
on such systems arises from spontaneous emission, in which photons are absorbed
by atoms and then re-scattered into undesired channels. In typical treatments
of atomic ensembles, it is assumed that this re-scattering occurs
independently, and at a rate given by a single isolated atom, which in turn
gives rise to standard limits of fidelity in applications such as quantum
memories or quantum gates. However, this assumption can be violated. In
particular, spontaneous emission of a collective atomic excitation can be
significantly suppressed through strong interference in...
Hasan, Zameer U.; Hemmer, Philip R.; Lee, Hwang; Migdall, Alan L.; Zhong, Tian; Kindem, Jonathan M.; Bartholomew, John G.; Rochman, Jake; Craiciu, Ioana; Miyazono, Evan; Faraon, Andrei
The integration of rare-earth ions in an on-chip photonic platform would enable quantum repeaters and scalable quantum networks. While ensemble-based quantum memories have been routinely realized, implementing single rare-earth ion qubit remains an outstanding challenge due to its weak photoluminescence. Here we demonstrate a nanophotonic platform consisting of yttrium vanadate (YVO) photonic crystal nanobeam resonators coupled to a spectrally dilute ensemble of Nd ions. The cavity acts as a memory when prepared with spectral hole burning, meanwhile it permits addressing of single ions when high-resolution spectroscopy is employed. For quantum memory, atomic frequency comb (AFC) protocol was implemented in a...
Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.
Double layer two-dimensional electron systems at high perpendicular magnetic field are used to realize magnetic tunnel junctions in which the electrons at the Fermi level in the two layers have either parallel or antiparallel spin magnetizations. In the antiparallel case the tunnel junction, at low temperatures, behaves as a nearly ideal spin diode. At elevated temperatures the diode character degrades as long-wavelength spin waves are thermally excited. These tunnel junctions provide a demonstration that the spin polarization of the electrons in the N=1 Landau level at filling factors ν=5/2 and 7/2 is essentially complete, and, with the aid of an...
Zhang, Yuhe; Jain, J. K.; Eisenstein, J. P.
In a bilayer system consisting of a composite-fermion Fermi sea in each layer, the tunnel current is exponentially suppressed at zero bias, followed by a strong peak at a finite bias voltage V_(max). This behavior, which is qualitatively different from that observed for the electron Fermi sea, provides fundamental insight into the strongly correlated non-Fermi liquid nature of the CF Fermi sea and, in particular, offers a window into the short-distance high-energy physics of this state. We identify the exciton responsible for the peak current and provide a quantitative account of the value of V_(max). The excitonic attraction is shown...
Brendel, Christian; Peano, Vittorio; Painter, Oskar; Marquardt, Florian
We show how the snowflake phononic crystal structure, which has been realized
experimentally recently, can be turned into a topological insulator for sound
waves. This idea, based purely on simple geometrical modifications, could be
readily implemented on the nanoscale.
Keller, Andrew J.; Dieterle, Paul B.; Fang, Michael; Berger, Brett; Fink, Johannes M.; Painter, Oskar
We present the fabrication and characterization of transmon qubits formed
from aluminum Josephson junctions on two different silicon-based substrates:
(i) high-resistivity silicon (Si) and (ii) silicon-on-insulator (SOI). Key to
the qubit fabrication process is the use of an anhydrous hydrofluoric vapor
process which removes silicon surface oxides without attacking aluminum, and in
the case of SOI substrates, selectively removes the lossy buried oxide
underneath the qubit region. For qubits with a transition frequency of
approximately $5$GHz we find qubit lifetimes and coherence times comparable to
those attainable on sapphire substrates ($T_{1,\text{Si}} = 27\mu$s,
$T_{2,\text{Si}} = 6.6\mu$s; $T_{1,\text{SOI}} = 3.5\mu$s, $T_{2,\text{SOI}} =
2.2\mu$s). This qubit fabrication process in principle permits co-fabrication
of...
Harter, J. W.; Zhao, Z. Y.; Yan, J.-Q.; Mandrus, D. G.; Hsieh, D.
Strong electron interactions can drive metallic systems toward a variety of well-known symmetry-broken phases, but the instabilities of correlated metals with strong spin-orbit coupling have only recently begun to be explored. We uncovered a multipolar nematic phase of matter in the metallic pyrochlore Cd_2Re_2O_7 using spatially resolved second-harmonic optical anisotropy measurements. Like previously discovered electronic nematic phases, this multipolar phase spontaneously breaks rotational symmetry while preserving translational invariance. However, it has the distinguishing property of being odd under spatial inversion, which is allowed only in the presence of spin-orbit coupling. By examining the critical behavior of the multipolar nematic order...
Miyazono, Evan; Craiciu, Ioana; Arbabi, Amir; Zhong, Tian; Faraon, Andrei
A scalable platform for on-chip optical quantum networks will rely on standard top-down nanofabrication techniques and solid-state emitters with long coherence times. We present a new hybrid platform that integrates amorphous silicon photonic waveguides and microresonators fabricated on top of a yttrium orthosilicate substrate doped with erbium ions. The quality factor of one such resonator was measured to exceed 100,000 and the ensemble cooperativity was measured to be 0.54. The resonator-coupled ions exhibited spontaneous emission rate enhancement and increased coupling to the input field, as required for further development of on-chip quantum light-matter interfaces.
Dahlsten, Oscar C. O.; Choi, Mahn-Soo; Braun, Daniel; Garner, Andrew J P; Yunger Halpern, Nicole; Vedral, Vlatko
We derive an equality for non-equilibrium statistical mechanics in finite-dimensional quantum systems. The equality concerns the worst-case work output of a time-dependent Hamiltonian protocol in the presence of a Markovian heat bath. It has the form 'worst-case work = penalty—optimum'. The equality holds for all rates of changing the Hamiltonian and can be used to derive the optimum by setting the penalty to 0. The optimum term contains the max entropy of the initial state, rather than the von Neumann entropy, thus recovering recent results from single-shot statistical mechanics. Energy coherences can arise during the protocol but are assumed not...
Paulisch, V.; González-Tudela, A.; Kimble, H. J.; Cirac, J. I.
Waveguide QED offers the possibility of generating strong coherent atomic interactions either through appropriate atomic configurations in the dissipative regime or in the bandgap regime. In this work, we show how to harness these interactions in order to herald the generation of highly entangled atomic states, which afterwards can be mapped to generate single mode multi-photonic states with high fidelities. We introduce two protocols for the preparation of the atomic states, we discuss their performance and compare them to previous proposals. In particular, we show that one of them reaches high probability of success for systems with many atoms but...
Farrelly, Terry; Brandão, Fernando G. S. L.; Cramer, Marcus
Thermal states are the bedrock of statistical physics. Nevertheless, when and how they actually arise in closed quantum systems is not fully understood. We consider this question for systems with local Hamiltonians on finite quantum lattices. In a first step, we show that states with exponentially decaying correlations equilibrate after a quantum quench. Then, we show that the equilibrium state is locally equivalent to a thermal state, provided that the free energy of the equilibrium state is sufficiently small and the thermal state has exponentially decaying correlations. As an application, we look at a related important question: When are thermal...
Khalique, Aeysha; Sanders, Barry C.
We explain how to share photons between two distant parties using concatenated entanglement swapping and assess performance according to the two-photon visibility as the figure of merit. From this analysis, we readily see the key generation rate and the quantum bit error rate as figures of merit for this scheme applied to quantum key distribution (QKD). Our model accounts for practical limitations, including higher-order photon pair events, dark counts, detector inefficiency, and photon losses. Our analysis shows that compromises are needed among the runtimes for the experiment, the rate of producing photon pairs, and the choice of detector efficiency. From...
Niu, Murphy Yuezhen; Sanders, Barry C.; Wong, Franco N. C.; Shapiro, Jeffrey H.
We propose an optical scheme, employing optical parametric down-converters interlaced with nonlinear sign gates (NSGs), that completely converts an n-photon Fock-state pump to n signal-idler photon pairs when the down-converters’ crystal lengths are chosen appropriately. The proof of this assertion relies on amplitude amplification, analogous to that employed in Grover search, applied to the full quantum dynamics of single-mode parametric down-conversion. When we require that all Grover iterations use the same crystal, and account for potential experimental limitations on crystal-length precision, our optimized conversion efficiencies reach unity for 1 ≤ n ≤ 5, after which they decrease monotonically for n...
Wilson, Justin H.; Pixley, J. H.; Goswami, Pallab; Das Sarma, S.
The gapless Bogoliubov-de Gennes (BdG) quasiparticles of a clean three dimensional spinless p_x + ip_y superconductor provide an intriguing example of a thermal Hall semimetal (ThSM) phase of Majorana-Weyl fermions; such a phase can support a large anomalous thermal Hall conductivity and protected surface Majorana-Fermi arcs at zero energy. We study the effects of quenched disorder on such a gapless topological phase by carrying out extensive numerical and analytical calculations on a lattice model for a disordered, spinless p_x + ip_y superconductor. Using the kernel polynomial method, we compute both average and typical density of states for the BdG quasiparticles,...
Bao, Ning; Remmen, Grant N.
We prove, for any state in a conformal field theory defined on a set of
boundary manifolds with corresponding classical holographic bulk geometry, that
for any bipartition of the boundary into two non-clopen sets, the density
matrix cannot be a direct product of the reduced density matrices on each
region of the bipartition. In particular, there must be entanglement across the
bipartition surface. We extend this no-go theorem to general, arbitrary
partitions of the boundary manifolds into non-clopen parts, proving that the
density matrix cannot be a direct product. This result gives a necessary
condition for states to potentially correspond to holographic duals.