Search results for "Quantum physic"
showing 10 items of 1596 documents
Entanglement-enhanced detection of single-photon scattering events
2013
The ability to detect the interaction of light and matter at the single-particle level is becoming increasingly important for many areas of science and technology. The absorption or emission of a photon on a narrow transition of a trapped ion can be detected with near unit probability, thereby enabling the realization of ultra-precise ion clocks and quantum information processing applications. Extending this sensitivity to broad transitions is challenging due to the difficulty of detecting the rapid photon scattering events in this case. Here, we demonstrate a technique to detect the scattering of a single photon on a broad optical transition with high sensitivity. Our approach is to use an…
Cavity QED of a leaky planar resonator coupled to an atom and an input single-photon pulse
2013
In contrast to the free-space evolution of an atom governed by a multi-mode interaction with the surrounding electromagnetic vacuum, the evolution of a cavity-QED system can be characterized by just three parameters, (i) atom-cavity coupling strength g, (ii) cavity relaxation rate \kappa, and (iii) atomic decay rate into the non-cavity modes \gamma. In the case of an atom inserted into a planar resonator with an input beam coupled from the outside, it has been shown by Koshino [Phys. Rev. A 73, 053814 (2006)] that these three parameters are determined not only by the atom and cavity characteristics, but also by the spatial distribution of the input pulse. By an ab-initio treatment, we gener…
Reducing quantum control for spin - spin entanglement distribution.
2009
We present a protocol that sets maximum stationary entanglement between remote spins through scattering of mobile mediators without initialization, post-selection or feedback of the mediators' state. No time-resolved tuning is needed and, counterintuitively, the protocol generates two-qubit singlet states even when classical mediators are used. The mechanism responsible for such effect is resilient against non-optimal coupling strengths and dephasing affecting the spins. The scheme uses itinerant particles and scattering centres and can be implemented in various settings. When quantum dots and photons are used a striking result is found: injection of classical mediators, rather than quantum…
Waveguide-QED-based measurement of a reservoir spectral density
2015
The spectral density (SD) function has a central role in the study of open quantum systems (OQSs). We discover a method allowing for a "static" measurement of the SD - i.e., it requires neither the OQS to be initially excited nor its time evolution tracked in time - which is not limited to the weak-coupling regime. This is achieved through one-dimensional photon scattering for a zero-temperature reservoir coupled to the OQS via the rotating wave approximation. We find that the SD profile is a universal simple function of the photon's reflectance and transmittance. As such, it can be straightforwardly inferred from photon's reflection and transmission spectra.
Local Sensing with the Multi-Level AC Stark Effect
2018
Analyzing weak microwave signals in the GHz regime is a challenging task if the signal level is very low and the photon energy widely undefined. A superconducting qubit can detect signals in the low photon regime, but due to its discrete level structure, it is only sensitive to photons of certain energies. With a multi-level quantum system (qudit) in contrast, the unknown signal frequency and amplitude can be deduced from the higher level AC Stark shift. The measurement accuracy is given by the signal amplitude, its detuning from the discrete qudit energy level structure and the anharmonicity. We demonstrate an energy sensitivity in the order of $10^{-3}$ with a measurement range of more th…
Spontaneous, collective coherence in driven, dissipative cavity arrays
2014
We study an array of dissipative tunnel-coupled cavities, each interacting with an incoherently pumped two-level emitter. For cavities in the lasing regime, we find correlations between the light fields of distant cavities, despite the dissipation and the incoherent nature of the pumping mechanism. These correlations decay exponentially with distance for arrays in any dimension but become increasingly long ranged with increasing photon tunneling between adjacent cavities. The interaction-dominated and the tunneling-dominated regimes show markedly different scaling of the correlation length which always remains finite due to the finite photon trapping time. We propose a series of observables…
Imaging Trapped Ion Structures via Fluorescence Cross-Correlation Detection
2021
Cross-correlation signals are recorded from fluorescence photons scattered in free space off a trapped ion structure. The analysis of the signal allows for unambiguously revealing the spatial frequency, thus the distance, as well as the spatial alignment of the ions. For the case of two ions we obtain from the cross-correlations a spatial frequency ${f}_{\text{spatial}}=1490\ifmmode\pm\else\textpm\fi{}{2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{8}_{\mathrm{syst}}\text{ }\text{ }{\mathrm{rad}}^{\ensuremath{-}1}$, where the statistical uncertainty improves with the integrated number of correlation events as ${N}^{\ensuremath{-}0.51\ifmmode\pm\else\textpm\fi{}0.06}$. We independently deter…
Theory and experimental verification of Kapitza–Dirac–Talbot–Lau interferometry
2009
Kapitza-Dirac-Talbot-Lau interferometry (KDTLI) has recently been established for demonstrating the quantum wave nature of large molecules. A phase space treatment permits us to derive closed equations for the near-field interference pattern, as well as for the Moire-type pattern that would arise if the molecules were to be treated as classical particles. The model provides a simple and elegant way to account for the molecular phase shifts related to the optical dipole potential as well as for the incoherent effect of photon absorption at the second grating. We present experimental results for different molecular masses, polarizabilities and absorption cross sections using fullerenes and fl…
Quantum error correction against photon loss using multi-component cat states
2016
We analyse a generalised quantum error correction code against photon loss where a logical qubit is encoded into a subspace of a single oscillator mode that is spanned by distinct multi-component cat states (coherent-state superpositions). We present a systematic code construction that includes the extension of an existing one-photon-loss code to higher numbers of losses. When subject to a photon loss (amplitude damping) channel, the encoded qubits are shown to exhibit a cyclic behaviour where the code and error spaces each correspond to certain multiples of losses, half of which can be corrected. As another generalisation we also discuss how to protect logical qudits against photon losses,…
Speeding up antidynamical Casimir effect with nonstationary qutrits
2017
The antidynamical Casimir effect (ADCE) is a term coined to designate the coherent annihilation of excitations due to resonant external perturbation of system parameters, allowing for extraction of quantum work from nonvacuum states of some field. Originally proposed for a two-level atom (qubit) coupled to a single cavity mode in the context of nonstationary quantum Rabi model, it suffered from very low transition rate and correspondingly narrow resonance linewidth. In this paper we show analytically and numerically that the ADCE rate can be increased by at least one order of magnitude by replacing the qubit by an artificial three-level atom (qutrit) in a properly chosen configuration. For …