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Zero Quantum Coherence

Antoine Reigue, Jake Iles-Smith, Fabian Lux, Léonard Monniello, Mathieu Bernard, Florent Margaillan, Aristide Lemaitre, Anthony Martinez, Dara P S McCutcheon, Jesper Mørk, Richard Hostein, Valia Voliotis
We investigate the temperature dependence of photon coherence properties through two-photon interference (TPI) measurements from a single quantum dot (QD) under resonant excitation. We show that the loss of indistinguishability is related only to the electron-phonon coupling and is not affected by spectral diffusion. Through these measurements and a complementary microscopic theory, we identify two independent separate decoherence processes, both of which are associated with phonons. Below 10 K, we find that the relaxation of the vibrational lattice is the dominant contribution to the loss of TPI visibility...
June 9, 2017: Physical Review Letters
D M Villeneuve, Paul Hockett, M J J Vrakking, Hiromichi Niikura
Electrons detached from atoms or molecules by photoionization carry information about the quantum state from which they originate, as well as the continuum states into which they are released. Generally, the photoelectron momentum distribution is composed of a coherent sum of angular momentum components, each with an amplitude and phase. Here we show, by using photoionization of neon, that a train of attosecond pulses synchronized with an infrared laser field can be used to disentangle these angular momentum components...
June 16, 2017: Science
Maja D Bachmann, Nityan Nair, Felix Flicker, Roni Ilan, Tobias Meng, Nirmal J Ghimire, Eric D Bauer, Filip Ronning, James G Analytis, Philip J W Moll
By introducing a superconducting gap in Weyl or Dirac semimetals, the superconducting state inherits the nontrivial topology of their electronic structure. As a result, Weyl superconductors are expected to host exotic phenomena, such as nonzero-momentum pairing due to their chiral node structure, or zero-energy Majorana modes at the surface. These are of fundamental interest to improve our understanding of correlated topological systems, and, moreover, practical applications in phase-coherent devices and quantum applications have been proposed...
May 2017: Science Advances
Naotaka Yoshikawa, Tomohiro Tamaya, Koichiro Tanaka
The electronic properties of graphene can give rise to a range of nonlinear optical responses. One of the most desirable nonlinear optical processes is high-harmonic generation (HHG) originating from coherent electron motion induced by an intense light field. Here, we report on the observation of up to ninth-order harmonics in graphene excited by mid-infrared laser pulses at room temperature. The HHG in graphene is enhanced by an elliptically polarized laser excitation, and the resultant harmonic radiation has a particular polarization...
May 19, 2017: Science
T Ota, M Hashisaka, K Muraki, T Fujisawa
Cross-correlation noise in electrical currents generated from a series connection of two quantum point contacts (QPCs), the injector and the detector, is described for investigating energy relaxation in quantum Hall edge channels at bulk filling factor [Formula: see text]. We address the importance of tuning the energy bias across the detector for this purpose. For a long channel with a macroscopic floating ohmic contact that thermalizes the electrons, the cross-correlation turns from negative values to the maximally positive value (identical noise in the two currents) by tuning the effective energy bias to zero...
June 7, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Carlos A Melo-Luna, Cristian E Susa, Andrés F Ducuara, Astrid Barreiro, John H Reina
Game theory is a well established branch of mathematics whose formalism has a vast range of applications from the social sciences, biology, to economics. Motivated by quantum information science, there has been a leap in the formulation of novel game strategies that lead to new (quantum Nash) equilibrium points whereby players in some classical games are always outperformed if sharing and processing joint information ruled by the laws of quantum physics is allowed. We show that, for a bipartite non zero-sum game, input local quantum correlations, and separable states in particular, suffice to achieve an advantage over any strategy that uses classical resources, thus dispensing with quantum nonlocality, entanglement, or even discord between the players' input states...
March 22, 2017: Scientific Reports
L D Contreras-Pulido, M Bruderer
One of the fundamental questions in quantum transport is how charge transfer through complex nanostructures is influenced by quantum coherence. We address this issue for linear triple quantum dots by comparing a Lindblad density matrix description with a Pauli rate equation approach and analyze the corresponding zero-frequency counting statistics of charge transfer. The impact of decaying coherences of the density matrix due to dephasing is also studied. Our findings reveal that the sensitivity to coherence shown by shot noise and skewness, in particular in the limit of large coupling to the drain reservoir, can be used to unambiguously evidence coherent processes involved in charge transport across triple quantum dots...
March 15, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Tobias F Sjolander, Michael C D Tayler, Arne Kentner, Dmitry Budker, Alexander Pines
We present a two-dimensional method for obtaining (13)C-decoupled, (1)H-coupled nuclear magnetic resonance (NMR) spectra in zero magnetic field using coherent spin-decoupling. The result is a spectrum determined only by the proton-proton J-coupling network. Detection of NMR signals in zero magnetic field requires at least two different nuclear spin species, but the proton J-spectrum is independent of isotopomer, thus potentially simplifying spectra and thereby improving the analytical capabilities of zero-field NMR...
March 21, 2017: Journal of Physical Chemistry Letters
Ya-Ju Song, Qing-Shou Tan, Le-Man Kuang
We investigate the possibility to control quantum evolution speed of a single dephasing qubit for arbitrary initial states by the use of periodic dynamical decoupling (PDD) pulses. It is indicated that the quantum speed limit time (QSLT) is determined by initial and final quantum coherence of the qubit, as well as the non-Markovianity of the system under consideration during the evolution when the qubit is subjected to a zero-temperature Ohmic-like dephasing reservoir. It is shown that final quantum coherence of the qubit and the non-Markovianity of the system can be modulated by PDD pulses...
March 8, 2017: Scientific Reports
Jordan N Nelson, Matthew D Krzyaniak, Noah E Horwitz, Brandon K Rugg, Brian T Phelan, Michael R Wasielewski
Photoinitiated subnanosecond electron transfer within covalently linked electron donor-acceptor molecules can result in the formation of a spin-correlated radical pair (SCRP) with a well-defined initial singlet spin configuration. Subsequent coherent mixing between the SCRP singlet and triplet ms = 0 spin states, the so-called zero quantum coherence (ZQC), is of potential interest in quantum information processing applications because the ZQC can be probed using pulse electron paramagnetic resonance (pulse-EPR) techniques...
March 14, 2017: Journal of Physical Chemistry. A
Evan Meyer-Scott, Johannes Tiedau, Georg Harder, Lynden K Shalm, Tim J Bartley
The statistical properties of photons are fundamental to investigating quantum mechanical phenomena using light. In multiphoton, two-mode systems, correlations may exist between outcomes of measurements made on each mode which exhibit useful properties. Correlation in this sense can be thought of as increasing the probability of a particular outcome of a measurement on one subsystem given a measurement on a correlated subsystem. Here, we show a statistical property we call "discorrelation", in which the probability of a particular outcome of one subsystem is reduced to zero, given a measurement on a discorrelated subsystem...
January 30, 2017: Scientific Reports
Jacob Linder, Morten Amundsen, Jabir Ali Ouassou
We demonstrate theoretically that microwave radiation applied to superconducting proximity structures controls the minigap and other spectral features in the density of states of normal and magnetic metals, respectively. Considering both a bilayer and Josephson junction geometry, we show that microwaves with frequency ω qualitatively alters the spectral properties of the system: inducing a series of resonances, controlling the minigap size Emg, and even replacing the minigap with a strong peak of quasiparticle accumulation at zero energy when ω = Emg...
December 16, 2016: Scientific Reports
Samuel F Cousin, Cyril Charlier, Pavel Kadeřávek, Thorsten Marquardsen, Jean-Max Tyburn, Pierre-Alain Bovier, Simone Ulzega, Thomas Speck, Dirk Wilhelm, Frank Engelke, Werner Maas, Dimitrios Sakellariou, Geoffrey Bodenhausen, Philippe Pelupessy, Fabien Ferrage
Nuclear magnetic resonance (NMR) is a ubiquitous branch of spectroscopy that can explore matter at the scale of an atom. Significant improvements in sensitivity and resolution have been driven by a steady increase of static magnetic field strengths. However, some properties of nuclei may be more favourable at low magnetic fields. For example, transverse relaxation due to chemical shift anisotropy increases sharply at higher magnetic fields leading to line-broadening and inefficient coherence transfers. Here, we present a two-field NMR spectrometer that permits the application of rf-pulses and acquisition of NMR signals in two magnetic centres...
December 7, 2016: Physical Chemistry Chemical Physics: PCCP
P V Pyshkin, Da-Wei Luo, Jun Jing, J Q You, Lian-Ao Wu
Holonomic quantum computation (HQC) may not show its full potential in quantum speedup due to the prerequisite of a long coherent runtime imposed by the adiabatic condition. Here we show that the conventional HQC can be dramatically accelerated by using external control fields, of which the effectiveness is exclusively determined by the integral of the control fields in the time domain. This control scheme can be realized with net zero energy cost and it is fault-tolerant against fluctuation and noise, significantly relaxing the experimental constraints...
November 25, 2016: Scientific Reports
Ying Li, Christos Argyropoulos
We demonstrate a plasmonic route to control the collective spontaneous emission of two-level quantum emitters. Superradiance and subradiance effects are observed over distances comparable to the operating wavelength inside plasmonic nanochannels. These plasmonic waveguides can provide an effective epsilon-near-zero operation in their cut-off frequency and Fabry-Pérot resonances at higher frequencies. The related plasmonic resonant modes are found to efficiently enhance the constructive (superradiance) or destructive (subradiance) interference between different quantum emitters located inside the waveguides...
November 14, 2016: Optics Express
Rajesh Dutta, Biman Bagchi
We study excitation transfer and migration in a one-dimensional lattice characterized by dynamic disorder. The diagonal and off-diagonal energy disorders arise from the coupling of system and bath. We consider both same bath (when baths are spatially correlated) and independent bath (when baths are completely uncorrelated) limits. In the latter case, all diagonal and off-diagonal bath coupling elements fluctuate independently of each other and the dynamics is complicated. We obtain time dependent population distribution by solving Kubo's quantum stochastic Liouville equation...
October 28, 2016: Journal of Chemical Physics
Michael Niklas, Mónica Benito, Sigmund Kohler, Gloria Platero
We analyze an AC-driven dimer chain connected to a strongly biased electron source and drain. It turns out that the resulting transport exhibits fingerprints of topology. They are particularly visible in the driving-induced current suppression and the Fano factor. Thus, shot noise measurements provide a topological phase diagram as a function of the driving parameters. The observed phenomena can be explained physically by a mapping to an effective time-independent Hamiltonian and the emergence of edge states...
November 11, 2016: Nanotechnology
William O Hutson, Austin P Spencer, Elad Harel
Vibrations play a critical role in many photochemical and photophysical processes in which excitations reside on the electronically excited state. However, difficulty in assigning signals from spectroscopic measurements uniquely to a specific electronic state, ground or otherwise, has exposed limitations to their physical interpretation. Here, we demonstrate the selective excitation of vibrational coherences on the ground electronic state through impulsive Raman scattering, whose weak fifth-order signal is resonantly enhanced by coupling to strong electronic transitions...
September 15, 2016: Journal of Physical Chemistry Letters
Yuhei Sekiguchi, Yusuke Komura, Shota Mishima, Touta Tanaka, Naeko Niikura, Hideo Kosaka
Spin echo is a fundamental tool for quantum registers and biomedical imaging. It is believed that a strong magnetic field is needed for the spin echo to provide long memory and high resolution, since a degenerate spin cannot be controlled or addressed under a zero magnetic field. While a degenerate spin is never subject to dynamic control, it is still subject to geometric control. Here we show the spin echo of a degenerate spin subsystem, which is geometrically controlled via a mediating state split by the crystal field, in a nitrogen vacancy centre in diamond...
2016: Nature Communications
Wei Niu, Ming Gao, Xuefeng Wang, Fengqi Song, Jun Du, Xinran Wang, Yongbing Xu, Rong Zhang
Quantum interference effects (QIEs) dominate the appearance of low-temperature resistivity minimum in colossal magnetoresistance manganites. The T(1/2) dependent resistivity under high magnetic field has been evidenced as electron-electron (e-e) interaction. However, the evidence of the other source of QIEs, weak localization (WL), still remains insufficient in manganites. Here we report on the direct experimental evidence of WL in QIEs observed in the single-crystal La0.7Sr0.3MnO3 (LSMO) ultrathin films deposited by laser molecular beam epitaxy...
2016: Scientific Reports
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