1 

Effect of arylamine holetransport units on the performance of blue polyspirobifulorene lightemitting diodes
The operation of blue lightemitting diodes based on polyspirobifluorene with a varying number of N,N,N′,N′ tetraaryldiamino biphenyl (TAD) holetransport units (HTUs) is investigated. Assuming that the electron transport is not affected by the incorporation of TAD units, model calculations predict that a concentration of 5% HTU leads to an optimal efficiency for this blueemitting polymer. However, experimentally an optimum performance is achieved for 10% TAD HTUs. Analysis of the transport and recombination shows that polymer lightemitting diodes with 5%, 7.5%, and 12.5% TAD units follow the predicted behavior. The enhanced performance of the polymer with 10% TAD originates from a decrease in the number of electron traps, which is typically a factor of three lower than the universal value found in many polymers. This reduced number of traps leads to a reduction of nonradiative recombination and exciton quenching at the cathode.

[Abstract]

2 

Switching dynamics in ferroelectric P(VDFTrFE) thin films
Switching, i.e., polarization reversal, of ferroelectric P(VDFTrFE) thin films has been investigated in a wide range of applied electric field and temperature. The measured polarization transients can be quantitatively described by a compressed exponential function as originally formulated by Kolmogorov, Avrami, and Ishibashi (the KAI model). The phenomenological parameters switching time and Avrami index are related to the velocity and morphology of the domain walls, respectively. We show that the switching time depends exponentially on the electric field as described by the Merz law. The experimentally obtained Avrami index is independent of temperature but decreases with applied electric field from 1.55 at low field to 1.0 at 300 MV/m, indicative of an outofequilibrium dynamics of the growing domains. Using a random walk model we demonstrate that the observed switching dynamics is in agreement with a domain growth mechanism where domains are circular at low electric field with few nucleation sites, whereas at high field irregular entangled domains are formed. The density of nucleation sites is extracted as 1.5% of the monomeric units in this work. Switching transients on capacitors where the nuclei density has been artificially increased exhibit onedimensionallike growth, as predicted by our model. cop. 2015 American Physical Society.

[Abstract]

3 

Charge transport in disordered semiconducting polymers driven by nuclear tunneling
The current densityvoltage (JV) characteristics of holeonly diodes based on poly(2methoxy, 5(2′ ethylhexyloxy)pphenylene vinylene) (MEHPPV) were measured at a wide temperature and field range. At high electric fields the temperature dependence of the transport vanishes, and all JV sweeps converge to a power law. Nuclear tunneling theory predicts a power law at high fields that scales with the Kondo parameter. To model the JV characteristics we have performed masterequation calculations to determine the dependence of charge carrier mobility on electric field, charge carrier density, temperature, and Kondo parameter, using nuclear tunneling transfer rates. We demonstrate that nuclear tunneling, unlike other semiclassical models, provides a consistent description of the charge transport for a large bias, temperature, and carrier density range. cop. 2016 authors. Published by the American Physical Society.

[Abstract]

4 

Modeling regionbased interconnection for interdependent networks
Various realworld networks interact with and depend on each other. The design of the interconnection between interacting networks is one of the main challenges to achieve a robust interdependent network. Due to cost considerations, network providers are inclined to interconnect nodes that are geographically close. Accordingly, we propose two topologies, the random geographic graph and the relative neighborhood graph, for the design of interconnection in interdependent networks that incorporates the geographic location of nodes. Differing from the onetoone interconnection studied in the literature, one node in one network can depend on an arbitrary number of nodes in the other network. We derive the average number of interdependent links for the two topologies, which enables their comparison. For the two topologies, we evaluate the impact of the interconnection structure on the robustness of interdependent networks against cascading failures. The two topologies are assessed on the realworld coupled Italian Internet and the electric transmission network. Finally, we propose the derivative of the largest mutually connected component with respect to the fraction of failed nodes as a robustness metric. This robustness metric quantifies the damage of the network introduced by a small fraction of initial failures well before the critical fraction of failures at which the whole network collapses. © 2016 American Physical Society.

[Abstract]

5 

Molecular Fountain
The resolution of any spectroscopic or interferometric experiment is ultimately limited by the total time a particle is interrogated. Here we demonstrate the first molecular fountain, a development which permits hitherto unattainably long interrogation times with molecules. In our experiments, ammonia molecules are decelerated and cooled using electric fields, launched upwards with a velocity between 1.4 and 1.9 m/s and observed as they fall back under gravity. A combination of quadrupole lenses and bunching elements is used to shape the beam such that it has a large position spread and a small velocity spread (corresponding to a transverse temperature of <10 μK and a longitudinal temperature of <1 μK) when the molecules are in free fall, while being strongly focused at the detection region. The molecules are in free fall for up to 266 ms, making it possible, in principle, to perform subHz measurements in molecular systems and paving the way for stringent tests of fundamental physics theories.

[Abstract]

6 

Scalable quantum circuit and control for a superconducting surface code
We present a scalable scheme for executing the errorcorrection cycle of a monolithic surfacecode fabric composed of fastfluxtunable transmon qubits with nearestneighbor coupling. An eightqubit unit cell forms the basis for repeating both the quantum hardware and coherent control, enabling spatial multiplexing. This control uses three fixed frequencies for all singlequbit gates and a unique frequencydetuning pattern for each qubit in the cell. By pipelining the interaction and readout steps of ancillabased X and Ztype stabilizer measurements, we can engineer detuning patterns that avoid all secondorder transmontransmon interactions except those exploited in controlledphase gates, regardless of fabric size. Our scheme is applicable to defectbased and planar logical qubits, including lattice surgery.

[Abstract]

7 

Quantum frequency conversion of single photons from a nitrogenvacancy center in diamond to telecommunication wavelengths
We report on the conversion to telecommunication wavelengths of single photons emitted by nitrogenvacancy (NV) defect in diamond. By means of different frequency generation, we convert spinselective photon at 637 nm, associated with the coherent NV zerophoton line, to the target wavelength of 1588 nm in the Ltelecommunication band. The succesful conversion is evidenced by timeresolved detection revealing a telecommunicationphoton lifetime identical to that of the original 637nm photon. Furthermore, we show by secondorder correlation measurements that the singlephoton statistics are preserved. The overall efficiency of this onestep conversion reaches 17% in our current setup, along with a signaltonoise ration of approximately 7 despite the low probability (<103) of an incident 637nm photon. This result shows the potential for efficient telecommunicationphotonNVcenter interfaces and marks an important step towards future longrange entanglementbased quantum networks.

[Abstract]

8 

Restless Tuneup of HighFidelity Qubit Gates
article 
2017

Author: 
Rol, M.A.
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Bultink, C.C.
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O'Brien, T.E.
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Jong, S.R. de
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Theis, L.S.
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Fu, X.
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Luthi, F.
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Vermeulen, R.F.L.
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Sterke, J.C. de
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Bruno, A.
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Deurloo, D.
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Schouten, R.N.
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Wilhelm, F.K.
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Dicarlo, L.

Keywords: 
High Tech Systems & Materials · Industrial Innovation · Observation, Weapon & Protection Systems · RT  Radar Technology · TS  Technical Sciences

We present a tuneup protocol for qubit gates with tenfold speedup over traditional methods reliant on qubit initialization by energy relaxation. This speedup is achieved by constructing a cost function for NelderMead optimization from realtime correlation of nondemolition measurements interleaving gate operations without pause. Applying the protocol on a transmon qubit achieves 0.999 average Clifford fidelity in one minute, as independently verified using randomized benchmarking and gateset tomography. The adjustable sensitivity of the cost function allows the detection of fractional changes in the gate error with a nearly constant signaltonoise ratio. The restless concept demonstrated can be readily extended to the tuneup of twoqubit gates and measurement operations.

[Abstract]

9 

Field effect enhancement in buffered quantum nanowire networks
article 
2018

Author: 
Krizek, F.
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Sestoft, J.E.
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Aseev, P.
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MartiSanchez, S.
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Vaitiekénas, S.
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Casparis, L.
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Khan, S.A.
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Liu, Y.
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Stankevic, T.
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Whiticar, A.M.
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Fursina, A.
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Boekhout, F.
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Koops, R.
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Uccelli, E.
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Kouwenhoven, L.P.
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Marcus, C.M.
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Arbiol, J.
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Krogstrup, P.

Keywords: 
Nanotechnology · High Tech Systems & Materials · Industrial Innovation

Semiconductor nanowires have shown great potential in various quantum transport experiments. However, realizing a scalable highquality nanowirebased platform that could lead to quantum information applications has been challenging. Here, we study the potential of selective area growth by molecular beam epitaxy of InAs nanowire networks grown on GaAsbased buffer layers, where Sb is used as a surfactant. The buffered geometry allows for substantial elastic strain relaxation and a strong enhancement of ﬁeld effect mobility. We show that the networks possess strong spinorbit interaction and long phasecoherence lengths with a temperature dependence indicating ballistic transport. With these ﬁndings, and the compatibility of the growth method with hybrid epitaxy, we conclude that the material platform fulﬁlls the requirements for a wide range of quantum experiments and applications.

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[Abstract]

10 

Ballistic supercurrent discretization and micrometerlong Josephson coupling in germanium
We fabricate Josephson fieldeffect transistors in germanium quantum wells contacted by superconducting aluminum and demonstrate supercurrents carried by holes that extend over junction lengths of several micrometers. In superconducting quantum point contacts we observe discretization of supercurrent, as well as FabryPerot resonances, demonstrating ballistic transport. The magnetic field dependence of the supercurrent follows a clear Fraunhoferlike pattern, and Shapiro steps appear upon microwave irradiation. Multiple Andreev reflections give rise to conductance enhancement and evidence a transparent interface, confirmed by analyzing the excess current. These demonstrations of ballistic superconducting transport are promising for hybrid quantum technology in germanium. A© 2019 American Physical Society.

[Abstract]

11 

Experimental error mitigation via symmetry verification in a variational quantum eigensolver
article 
2019

Author: 
Sagastizabal, R.
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BonetMonroig, X.
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Singh, M.
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Rol, M.A.
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Bultink, C.C.
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Fu, X.
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Price, C.H.
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Ostroukh, V.P.
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Muthusubramanian, N.
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Bruno, A.
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Beekman, M.
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Haider, N.
·
O'Brien, T.E.
·
Dicarlo, L.

Keywords: 
Convex optimization · Errors · Ground state · Quantum theory · Qubits · State estimation · Variational techniques · Error mitigation · Experimental errors · Experimental estimations · Full density matrix · Groundstate energies · Hydrogen molecule · Single excitation · Verification techniques · Excited states



12 

Entanglement between a Diamond Spin Qubit and a Photonic TimeBin Qubit at Telecom Wavelength
article 
2019

Author: 
Tchebotareva, A.
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Hermans, S.L.N.
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Humphreys, P.C.
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Voigt, D.
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Harmsma, P.J.
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Cheng, L.K.
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Verlaan, A.L.
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Dijkhuizen, N.
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Jong, W. de
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Dréau, A.
·
Hanson, R.

Keywords: 
Nonlinear optics · Optical quantum information processing · Quantum entanglement · Quantum networks · Communication networks · Photon pairs · Parametric downconversion · Electronics · High Tech Systems & Materials · Industrial Innovation

We report on the realization and verification of quantum entanglement between a nitrogenvacancy electron spin qubit and a telecomband photonic qubit. First we generate entanglement between the spin qubit and a 637 nm photonic timebin qubit, followed by photonic quantum frequency conversion that transfers the entanglement to a 1588 nm photon. We characterize the resulting state by correlation measurements in different bases and find a lower bound to the Bell state fidelity of > 0.77 + 0.03. This result presents an important step towards extending quantum networks via optical fiber infrastructure

[Abstract]

13 

Fast, HighFidelity ConditionalPhase Gate Exploiting Leakage Interference in Weakly Anharmonic Superconducting Qubits
article 
2019

Author: 
Rol, M.A.
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Battistel, F.
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Malinowski, F.K.
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Bultink, C.C.
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Tarasinski, B.M.
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Vollmer, R.
·
Haider, S.N.
·
Muthusubramanian, N.
·
Bruno, A.
·
Terhal, B.M.
·
Dicarlo, L.

Keywords: 
Atomic physics · Physics · Flux control · High frequency HF · Highfidelity · Leakage interferences · Phase gates · Speed limit · Superconducting qubits · Timescales · Qubits

Conditionalphase (cz) gates in transmons can be realized by flux pulsing computational states towards resonance with noncomputational ones. We present a 40 ns cz gate based on a bipolar flux pulse suppressing leakage (0.1%) by interference and approaching the speed limit set by exchange coupling. This pulse harnesses a builtin echo to enhance fidelity (99.1%) and is robust to longtimescale distortion in the fluxcontrol line, ensuring repeatability. Numerical simulations matching experiment show that fidelity is limited by highfrequency dephasing and leakage by shorttimescale distortion. © 2019 American Physical Society.

[Abstract]
