QUROPE Quantum Information Processing and Communication in Europe

Author(s): Henrik P. Lüschen, Sebastian Scherg, Thomas Kohlert, Michael Schreiber, Pranjal Bordia, Xiao Li, S. Das Sarma, and Immanuel Bloch

A single-particle mobility edge (SPME) marks a critical energy separating extended from localized states in a quantum system. In one-dimensional systems with uncorrelated disorder, a SPME cannot exist, since all single-particle states localize for arbitrarily weak disorder strengths. However, in a q...

[Phys. Rev. Lett. 120, 160404] Published Thu Apr 19, 2018

Author(s): Igor Ferrier-Barbut, Matthias Wenzel, Fabian Böttcher, Tim Langen, Mathieu Isoard, Sandro Stringari, and Tilman Pfau

We report on the observation of the scissors mode of a single dipolar quantum droplet. The existence of this mode is due to the breaking of the rotational symmetry by the dipole-dipole interaction, which is fixed along an external homogeneous magnetic field. By modulating the orientation of this mag...

[Phys. Rev. Lett. 120, 160402] Published Wed Apr 18, 2018

Author(s): Murphy Yuezhen Niu, Isaac L. Chuang, and Jeffrey H. Shapiro

We prove that universal quantum computation can be realized—using only linear optics and χ(2) (three-wave mixing) interactions—in any (n+1)-dimensional qudit basis of the n-pump-photon subspace. First, we exhibit a strictly universal gate set for the qubit basis in the one-pump-photon subspace. Next...

[Phys. Rev. Lett. 120, 160502] Published Wed Apr 18, 2018

Author(s): J. S. Pedernales, M. Beau, S. M. Pittman, I. L. Egusquiza, L. Lamata, E. Solano, and A. del Campo

We introduce an exact mapping between the Dirac equation in (1+1)-dimensional curved spacetime (DCS) and a multiphoton quantum Rabi model (QRM). A background of a (1+1)-dimensional black hole requires a QRM with one- and two-photon terms that can be implemented in a trapped ion for the quantum simul...

[Phys. Rev. Lett. 120, 160403] Published Tue Apr 17, 2018

Author(s): Rui Han, Gerd Leuchs, and Markus Grassl

When quantum states are used to send classical information, the receiver performs a measurement on the signal states. The amount of information extracted is often not optimal due to the receiver’s measurement scheme and experimental apparatus. For quantum nondemolition measurements, there is potenti...

[Phys. Rev. Lett. 120, 160501] Published Tue Apr 17, 2018

Author(s): A. M. Piekarska and T. K. Kopeć

We study disordered interacting bosons described by the Bose-Hubbard model with Gaussian-distributed random tunneling amplitudes. It is shown that the off-diagonal disorder induces a spin-glass-like ground state, characterized by randomly frozen quantum-mechanical U(1) phases of bosons. To access cr...

[Phys. Rev. Lett. 120, 160401] Published Mon Apr 16, 2018

Author(s): Nina Megier, Walter T. Strunz, Carlos Viviescas, and Kimmo Luoma

We derive a family of Gaussian non-Markovian stochastic Schrödinger equations for the dynamics of open quantum systems. The different unravelings correspond to different choices of squeezed coherent states, reflecting different measurement schemes on the environment. Consequently, we are able to giv...

[Phys. Rev. Lett. 120, 150402] Published Fri Apr 13, 2018

Author(s): Yen-Hsiang Lin, Long B. Nguyen, Nicholas Grabon, Jonathan San Miguel, Natalia Pankratova, and Vladimir E. Manucharyan

Long-lived transitions occur naturally in atomic systems due to the abundance of selection rules inhibiting spontaneous emission. By contrast, transitions of superconducting artificial atoms typically have large dipoles, and hence their lifetimes are determined by the dissipative environment of a ma...

[Phys. Rev. Lett. 120, 150503] Published Fri Apr 13, 2018

Author(s): N. Earnest, S. Chakram, Y. Lu, N. Irons, R. K. Naik, N. Leung, L. Ocola, D. A. Czaplewski, B. Baker, Jay Lawrence, Jens Koch, and D. I. Schuster

We realize a Λ system in a superconducting circuit, with metastable states exhibiting lifetimes up to 8 ms. We exponentially suppress the tunneling matrix elements involved in spontaneous energy relaxation by creating a “heavy” fluxonium, realized by adding a capacitive shunt to the original circuit...

[Phys. Rev. Lett. 120, 150504] Published Fri Apr 13, 2018

Author(s): Fabio Anza, Christian Gogolin, and Marcus Huber

Under unitary time evolution, expectation values of physically reasonable observables often evolve towards the predictions of equilibrium statistical mechanics. The eigenstate thermalization hypothesis (ETH) states that this is also true already for individual energy eigenstates. Here we aim at eluc...

[Phys. Rev. Lett. 120, 150603] Published Fri Apr 13, 2018

Author(s): Ge Bai and Giulio Chiribella

The performance of a quantum device for an infinite set of inputs could be evaluated by preparing a single entangled state and performing a single measurement on the output.

[Phys. Rev. Lett. 120, 150502] Published Thu Apr 12, 2018

Author(s): Hyukjoon Kwon, Hyunseok Jeong, David Jennings, Benjamin Yadin, and M. S. Kim

In thermodynamics, quantum coherences—superpositions between energy eigenstates—behave in distinctly nonclassical ways. Here we describe how thermodynamic coherence splits into two kinds—“internal” coherence that admits an energetic value in terms of thermodynamic work, and “external” coherence that...

[Phys. Rev. Lett. 120, 150602] Published Thu Apr 12, 2018

Author(s): Michael H. Kolodrubetz, Frederik Nathan, Snir Gazit, Takahiro Morimoto, and Joel E. Moore

We explore adiabatic pumping in the presence of a periodic drive, finding a new phase in which the topologically quantized pumped quantity is energy rather than charge. The topological invariant is given by the winding number of the micromotion with respect to time within each cycle, momentum, and a...

[Phys. Rev. Lett. 120, 150601] Published Wed Apr 11, 2018

Author(s): Shai Machnes, Elie Assémat, David Tannor, and Frank K. Wilhelm

Quantum computation places very stringent demands on gate fidelities, and experimental implementations require both the controls and the resultant dynamics to conform to hardware-specific constraints. Superconducting qubits present the additional requirement that pulses must have simple parameteriza...

[Phys. Rev. Lett. 120, 150401] Published Mon Apr 09, 2018

Author(s): Meghana Raghunandan, Jörg Wrachtrup, and Hendrik Weimer

The sensing of external fields using quantum systems is a prime example of an emergent quantum technology. Generically, the sensitivity of a quantum sensor consisting of N independent particles is proportional to N. However, interactions invariably occurring at high densities lead to a breakdown of ...

[Phys. Rev. Lett. 120, 150501] Published Mon Apr 09, 2018

Author(s): Tomasz Wasak and Jan Chwedeńczuk

We propose an experiment, where the Bell inequality is violated in a many-body system of massive particles. The source of correlated atoms is a spinor F=1 Bose-Einstein condensate residing in an optical lattice. We characterize the complete procedure—the local operations, the measurements, and the i...

[Phys. Rev. Lett. 120, 140406] Published Fri Apr 06, 2018

Author(s): Johannes Bülte, Adam Bednorz, Christoph Bruder, and Wolfgang Belzig

The development of solid-state quantum technologies requires the understanding of quantum measurements in interacting, nonisolated quantum systems. In general, a permanent coupling of detectors to a quantum system leads to memory effects that have to be taken into account in interpreting the measure...

[Phys. Rev. Lett. 120, 140407] Published Fri Apr 06, 2018

Author(s): R. V. Nery, M. M. Taddei, R. Chaves, and L. Aolita

Theoretical work on classical-quantum causal networks and experiments on entangled photons demonstrate that quantum steering is a stronger form of nonlocality than previously thought.

[Phys. Rev. Lett. 120, 140408] Published Fri Apr 06, 2018

Author(s): Anton Frisk Kockum, Göran Johansson, and Franco Nori

In quantum-optics experiments with both natural and artificial atoms, the atoms are usually small enough that they can be approximated as pointlike compared to the wavelength of the electromagnetic radiation with which they interact. However, superconducting qubits coupled to a meandering transmissi...

[Phys. Rev. Lett. 120, 140404] Published Thu Apr 05, 2018

Author(s): Yuan Cao, Yu-Huai Li, Wen-Jie Zou, Zheng-Ping Li, Qi Shen, Sheng-Kai Liao, Ji-Gang Ren, Juan Yin, Yu-Ao Chen, Cheng-Zhi Peng, and Jian-Wei Pan

Quantum entanglement was termed “spooky action at a distance” in the well-known paper by Einstein, Podolsky, and Rosen. Entanglement is expected to be distributed over longer and longer distances in both practical applications and fundamental research into the principles of nature. Here, we present ...

[Phys. Rev. Lett. 120, 140405] Published Thu Apr 05, 2018