570 research outputs found
Sub Decoherence Time Generation and Detection of Orbital Entanglement
Recent experiments have demonstrated sub decoherence time control of
individual single-electron orbital qubits. Here we propose a quantum dot based
scheme for generation and detection of pairs of orbitally entangled electrons
on a timescale much shorter than the decoherence time. The electrons are
entangled, via two-particle interference, and transferred to the detectors
during a single cotunneling event, making the scheme insensitive to charge
noise. For sufficiently long detector dot lifetimes, cross-correlation
detection of the dot charges can be performed with real-time counting
techniques, opening up for an unambiguous short-time Bell inequality test of
orbital entanglement.Comment: 5 pages, 2 figures, 3 pages supplemental materia
Photon counting statistics of a microwave cavity
The development of microwave photon detectors is paving the way for a wide
range of quantum technologies and fundamental discoveries involving single
photons. Here, we investigate the photon emission from a microwave cavity and
find that distribution of photon waiting times contains information about
few-photon processes, which cannot easily be extracted from standard
correlation measurements. The factorial cumulants of the photon counting
statistics are positive at all times, which may be intimately linked with the
bosonic quantum nature of the photons. We obtain a simple expression for the
rare fluctuations of the photon current, which is helpful in understanding
earlier results on heat transport statistics and measurements of work
distributions. Under non-equilibrium conditions, where a small temperature
gradient drives a heat current through the cavity, we formulate a
fluctuation-dissipation relation for the heat noise spectra. Our work suggests
a number of experiments for the near future, and it offers theoretical
questions for further investigation.Comment: 16 pages, 3 figures, final version as published in Phys. Rev.
Nanoscale Quantum Calorimetry with Electronic Temperature Fluctuations
Motivated by the recent development of fast and ultra-sensitive thermometry
in nanoscale systems, we investigate quantum calorimetric detection of
individual heat pulses in the sub-meV energy range. We propose a hybrid
superconducting injector-calorimeter set-up, with the energy of injected pulses
carried by tunneling electrons. Treating all heat transfer events
microscopically, we analyse the statistics of the calorimeter temperature
fluctuations and derive conditions for an accurate measurement of the heat
pulse energies. Our results pave the way for novel, fundamental quantum
thermodynamics experiments, including calorimetric detection of single
microwave photons.Comment: 6 pages, 3 figures plus supplemental material, 8 pages, 1 figur
Energy and temperature fluctuations in the single electron box
In mesoscopic and nanoscale systems at low temperatures, charge carriers are
typically not in thermal equilibrium with the surrounding lattice. The
resulting, non-equilibrium dynamics of electrons has only begun to be explored.
Experimentally the time-dependence of the electron temperature (deviating from
the lattice temperature) has been investigated in small metallic islands.
Motivated by these experiments we investigate theoretically the electronic
energy and temperature fluctuations in a metallic island in the Coulomb
blockade regime, tunnel coupled to an electronic reservoir, i.e. a single
electron box. We show that electronic quantum tunnelling between the island and
the reservoir, in the absence of any net charge or energy transport, induces
fluctuations of the island electron temperature. The full distribution of the
energy transfer as well as the island temperature is derived within the
framework of full counting statistics. In particular, the low-frequency
temperature fluctuations are analysed, fully accounting for charging effects
and non-zero reservoir temperature. The experimental requirements for measuring
the predicted temperature fluctuations are discussed.Comment: 20 pages, 4 figures, submitted to NJP special issue on Quantum
Thermodynamic
How Can Idea Campaigns Generate Ideas to Trigger Innovation?
Issue of study: The starting point for innovation is ideas, which can be seen as fuel to the innovation process as it supplies the innovation funnel with new or improved concepts that finally may spark innovation. There is a vast literature on the success of a few radical ideation methods and the use of creativity tools, while few have dealt with the use and effects of ideation approaches in practice. The idea for this master's thesis initially came from E.ON, a large utility company, which expressed a need to address the problem of internal ideation and how to take advantage of employees’ ideas to trigger innovation. Tapping into the creativity of employees and collecting their ideas is, in fact, a general desire of companies. However, managing ideation is a common challenge for large organisations. This is because ideation is often done autonomously in smaller organisations, whereas in large organisations a more structured approach towards idea management is needed in order to attain employees’ ideas. Purpose: The purpose of this thesis is to increase the understanding of how large organisations in general, and E.ON in particular, can conduct an idea campaign successfully in the front end of innovation Methodology: Based on the purpose of this study, a qualitative case study with a deductive approach was chosen for this thesis. The data collection mainly includes responses gathered from surveys and interviews with representatives at pre-study companies, as well as with E.ON employees. Conclusions: Six key factors for managing ideation, namely communication, collaboration, incentives, innovation climate, management support, and idea management, have been identified during the course of this master’s thesis. These factors have been studied in literature and then been validated as important in a pre-study including six large Swedish companies, as well as in a case study conducted at E.ON. All of the key factors are considered to be important for managing ideation successfully in large organisations. Based on the identified key factors, an Idea Campaign Framework for how to conduct an idea campaign successfully was developed in this thesis. The framework as a whole includes three phases of ideation: ideation planning, ideation execution and ideation follow up. The main focus in this thesis has been on the execution phase, which was developed to help large organisations to conduct an idea campaign successfully. The execution phase illustrates how key factors should be addressed in order to trigger certain features, which in turn would lead to desired effects of a successful idea campaign. The Idea Campaign Framework has been empirically tested at E.ON in Malmö, through the launch of an idea competition called ‘Bright Ideas’. The idea competition was launched during two weeks in the spring of 2013 and resulted in 160 ideas. The empirical evidence from the test at the case company conclude that the elements in the Idea Campaign Framework are important to consider in attaining employees’ ideas in large organisations. To conclude, the framework may be used as a guide for how to conduct an idea campaign successfully in order to attain employees’ ideas and feed the innovation funnel
Heat Pulses in Electron Quantum Optics
Electron quantum optics aims to realize ideas from the quantum theory of
light with the role of photons being played by charge pulses in electronic
conductors. Experimentally, the charge pulses are excited by time-dependent
voltages, however, one could also generate heat pulses by heating and cooling
an electrode. Here, we explore this intriguing idea by formulating a Floquet
scattering theory of heat pulses in mesoscopic conductors. The adiabatic
emission of heat pulses leads to a heat current that in linear response is
given by the thermal conductance quantum. However, we also find a
high-frequency component, which ensures that the fluctuation-dissipation
theorem for heat currents, whose validity has been debated, is fulfilled. The
heat pulses are uncharged, and we probe their electron-hole content by
evaluating the partition noise in the outputs of a quantum point contact. We
also employ a Hong--Ou--Mandel setup to examine if the pulses bunch or
antibunch. Finally, to generate an electric current, we use a Mach--Zehnder
interferometer that breaks the electron-hole symmetry and thereby enables a
thermoelectric effect. Our work paves the way for systematic investigations of
heat pulses in mesoscopic conductors, and it may stimulate future experiments.Comment: 6+5 pages, 4 figure
Early events in insulin fibrillization studied by time-lapse atomic force microscopy
The importance of understanding the mechanism of protein aggregation into
insoluble amyloid fibrils relies not only on its medical consequences, but also
on its more basic properties of self--organization. The discovery that a large
number of uncorrelated proteins can form, under proper conditions, structurally
similar fibrils has suggested that the underlying mechanism is a general
feature of polypeptide chains. In the present work, we address the early events
preceeding amyloid fibril formation in solutions of zinc--free human insulin
incubated at low pH and high temperature. Aside from being a easy--to--handle
model for protein fibrillation, subcutaneous aggregation of insulin after
injection is a nuisance which affects patients with diabetes. Here, we show by
time--lapse atomic force microscopy (AFM) that a steady-state distribution of
protein oligomers with an exponential tail is reached within few minutes after
heating. This metastable phase lasts for few hours until aggregation into
fibrils suddenly occurs. A theoretical explanation of the oligomer
pre--fibrillar distribution is given in terms of a simple
coagulation--evaporation kinetic model, in which concentration plays the role
of a critical parameter. Due to high resolution and sensitivity of AFM
technique, the observation of a long-lasting latency time should be considered
an actual feature of the aggregation process, and not simply ascribed to
instrumental inefficency. These experimental facts, along with the kinetic
model used, claim for a critical role of thermal concentration fluctuations in
the process of fibril nucleation
Dynamical quantum phase transitions in strongly correlated two-dimensional spin lattices following a quench
Dynamical quantum phase transitions are at the forefront of current efforts to understand quantum matter out of equilibrium. Except for a few exactly solvable models, predictions of these critical phenomena typically rely on advanced numerical methods. However, those approaches are mostly restricted to one dimension, making investigations of two-dimensional systems highly challenging. Here, we present evidence of dynamical quantum phase transitions in strongly correlated spin lattices in two dimensions. To this end, we apply our recently developed cumulant method [Phys. Rev. X11, 041018 (2021)] to determine the zeros of the Loschmidt amplitude in the complex plane of time, and we predict the crossing points of the thermodynamic lines of zeros with the real-time axis, where dynamical quantum phase transitions occur. We find the critical times of a two-dimensional quantum Ising lattice and the XYZ model with ferromagnetic or antiferromagnetic couplings. We also show how dynamical quantum phase transitions can be predicted by measuring the initial energy fluctuations, for example in quantum simulators or other engineered quantum systems.Peer reviewe
Determination of Dynamical Quantum Phase Transitions in Strongly Correlated Many-Body Systems Using Loschmidt Cumulants
Dynamical phase transitions extend the notion of criticality to nonstationary settings and are characterized by sudden changes in the macroscopic properties of time-evolving quantum systems. Investigations of dynamical phase transitions combine aspects of symmetry, topology, and nonequilibrium physics; however, progress has been hindered by the notorious difficulties of predicting the time evolution of large, interacting quantum systems. Here, we tackle this outstanding problem by determining the critical times of interacting many-body systems after a quench using Loschmidt cumulants. Specifically, we investigate dynamical topological phase transitions in the interacting Kitaev chain and in the spin-1 Heisenberg chain. To this end, we map out the thermodynamic lines of complex times, where the Loschmidt amplitude vanishes, and identify the intersections with the imaginary axis, which yield the real critical times after a quench. For the Kitaev chain, we can accurately predict how the critical behavior is affected by strong interactions, which gradually shift the time at which a dynamical phase transition occurs. We also discuss the experimental perspectives of predicting the first critical time of a quantum many-body system by measuring the energy fluctuations in the initial state, and we describe the prospects of implementing our method on a near-term quantum computer with a limited number of qubits. Our work demonstrates that Loschmidt cumulants are a powerful tool to unravel the far-from-equilibrium dynamics of strongly correlated many-body systems, and our approach can immediately be applied in higher dimensions.Dynamical phase transitions extend the notion of criticality to nonstationary settings and are characterized by sudden changes in the macroscopic properties of time-evolving quantum systems. Investigations of dynamical phase transitions combine aspects of symmetry, topology, and nonequilibrium physics; however, progress has been hindered by the notorious difficulties of predicting the time evolution of large, interacting quantum systems. Here, we tackle this outstanding problem by determining the critical times of interacting many-body systems after a quench using Loschmidt cumulants. Specifically, we investigate dynamical topological phase transitions in the interacting Kitaev chain and in the spin-1 Heisenberg chain. To this end, we map out the thermodynamic lines of complex times, where the Loschmidt amplitude vanishes, and identify the intersections with the imaginary axis, which yield the real critical times after a quench. For the Kitaev chain, we can accurately predict how the critical behavior is affected by strong interactions, which gradually shift the time at which a dynamical phase transition occurs. We also discuss the experimental perspectives of predicting the first critical time of a quantum many-body system by measuring the energy fluctuations in the initial state, and we describe the prospects of implementing our method on a near-term quantum computer with a limited number of qubits. Our work demonstrates that Loschmidt cumulants are a powerful tool to unravel the far-from-equilibrium dynamics of strongly correlated many-body systems, and our approach can immediately be applied in higher dimensions.Peer reviewe
- …