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Now showing items 31-40 of 75
Aufsatz
Fabrication of highly dense arrays of nanocrystalline diamond nanopillars with integrated silicon-vacancy color centers during the growth
(2019-11-06)
Highly dense arrays of diamond nanopillars have been fabricated using nanocrystalline diamond films (NCD) as the starting material. The fabrication process consisted of electron beam lithography (EBL), aluminum mask deposition and inductively coupled O2 plasma reactive ion etching. The EBL pattern fidelity was enhanced by proximity corrections and dose variations. Optical characterizations of the arrays indicated the incorporation of silicon-vacancy centers during NCD growth as well as enhanced fluorescence and ...
Aufsatz
High-precision force sensing using a single trapped ion
(2016-06-16)
We introduce quantum sensing schemes for measuring very weak forces with a single trapped ion. They use the spin-motional coupling induced by the laser-ion interaction to transfer the relevant force information to the spin-degree of freedom. Therefore, the force estimation is carried out simply by observing the Ramsey-type oscillations of the ion spin states. Three quantum probes are considered, which are represented by systems obeying the Jaynes-Cummings, quantum Rabi (in 1D) and Jahn-Teller (in 2D) models. By using ...
Aufsatz
Tunneling time in attosecond experiment for hydrogen atom
(2018-06-01)
Tunneling and tunneling time are hot debated and very interesting issues because of their fundamental role in the quantum mechanics. The measurement of the tunneling time in today's attosecond and strong field (low-frequency) experiments, despite its controversial discussion offers a fruitful opportunity to understand the time measurement and the role of time in quantum mechanics. In previous work Kullie (2015 Phys. Rev. A 92, 052118), we suggested a model and derived a simple relation to calculate the tunneling time, ...
Aufsatz
Transient non-confining potentials for speeding up a single ion heat pump
(2018-10-10)
We propose speeding up a single ion heat pump based on a tapered ion trap. If a trapped ion is excited in an oscillatory motion axially the radial degrees of freedom are cyclically expanded and compressed such that heat can be pumped between two reservoirs coupled to the ion at the turning points of oscillation. Through the use of invariant-based inverse engineering we can speed up the process without sacrificing the efficiency of each heat pump cycle. This additional control can be supplied with additional control ...
Aufsatz
Reservoir engineering using quantum optimal control for qubit reset
(2019-09-24)
We determine how to optimally reset a superconducting qubit which interacts with a thermal environment in such a way that the coupling strength is tunable. Describing the system in terms of a time-local master equation with time-dependent decay rates and using quantum optimal control theory, we identify temporal shapes of tunable level splittings which maximize the efficiency of the reset protocol in terms of duration and error. Time-dependent level splittings imply a modification of the system-environment coupling, ...
Aufsatz
Beating the limits with initial correlations
(2017-11-28)
Fast and reliable reset of a qubit is a key prerequisite for any quantum technology. For real world open quantum systems undergoing non-Markovian dynamics, reset implies not only purification, but in particular erasure of initial correlations between qubit and environment. Here, we derive optimal reset protocols using a combination of geometric and numerical control theory. For factorizing initial states, we find a lower limit for the entropy reduction of the qubit as well as a speed limit. The time-optimal solution ...
Aufsatz
High-Purity Triggered Single-Photon Emission from Symmetric Single InAs/InP Quantum Dots around the Telecom C-Band Window
(2019-11-07)
The authors demonstrate pure triggered single‐photon emission from quantum dots (QDs) around the telecommunication C‐band window, with characteristics preserved under non‐resonant excitation at saturation, that is, the highest possible, lifetime‐limited emission rates. The direct measurement of emission dynamics reveals photoluminescence decay times in the range of (1.7–1.8) ns corresponding to maximal photon generation rates exceeding 0.5 GHz. The measurements of the second‐order correlation function exhibit, for ...
Aufsatz
Direct evidence for radiative charge transfer after inner-shell excitation and ionization of large clusters
(2018-01-16)
We directly observe radiative charge transfer (RCT) in Ne clusters by dispersed vacuum-ultraviolet photon detection. The doubly ionized Ne^2+ – Ne_n-1 initial states of RCT are populated after resonant 1s–3p photoexcitation or 1s photoionization of Ne_n clusters with {n} \approx 2800. These states relax further producing Ne^+ – Ne^+ – Ne_n-2 final states, and the RCT photon is emitted. Ab initio calculations assign the observed RCT signal to the Ne^2+(2p^-2 [^1D]) - Ne_n-1 initial state, while transitions from other ...
Aufsatz
Tunneling Time in Attosecond Experiments and Time Operator in Quantum Mechanics
(2018-10-08)
Attosecond science is of a fundamental interest in physics. The measurement of the tunneling time in attosecond experiments, offers a fruitful opportunity to understand the role of time in quantum mechanics (QM). We discuss in this paper our tunneling time model in relation to two time operator definitions introduced by Bauer and Aharonov–Bohm. We found that both definitions can be generalized to the same type of time operator. Moreover, we found that the introduction of a phenomenological parameter by Bauer to fit ...
Aufsatz
Quantum optimal control of the dissipative production of a maximally entangled state
(2018-12-14)
Entanglement generation can be robust against certain types of noise in approaches that deliberately incorporate dissipation into the system dynamics. The presence of additional dissipation channels may, however, limit fidelity and speed of the process. Here we show how quantum optimal control techniques can be used to both speed up the entanglement generation and increase the fidelity in a realistic setup, whilst respecting typical experimental limitations. For the example of entangling two trapped ion qubits (Lin ...