Electron Shelving Research Articles

Resonant fluorescence of a bichromatically driven three-level atom with the electron shelving effect

Resonant fluorescence of a bichromatically driven three-level atom with the electron shelving effect

Long-Lifetime Optical Trapping of a 40Ca+ Ion

Abstract We have experimentally achieved the all-optical trapping of a 40Ca+ ion. An optical dipole trap was established using a high-power, far-detuned, tightly focused laser with a wavelength of 532 nm. The single 40Ca+ ion was trapped without any RF fields and demonstrated a long lifetime of over 3 s. In this experiment, we implemented several measures to improve the optical trapping probability, including focusing the dipole beam waist near the diffraction limit, precisely compensating for stray electric fields, and mitigating electron shelving in metastable states. The optical trapping of a 40Ca+ ion eliminates the influence of micromotion induced by RF fields, potentially paving the way for development of all-optical trapping ion optical clocks.

Electron shelving of a superconducting artificial atom

Interfacing long-lived qubits with propagating photons is a fundamental challenge in quantum technology. Cavity and circuit quantum electrodynamics (cQED) architectures rely on an off-resonant cavity, which blocks the qubit emission and enables a quantum non-demolition (QND) dispersive readout. However, no such buffer mode is necessary for controlling a large class of three-level systems that combine a metastable qubit transition with a bright cycling transition, using the electron shelving effect. Here we demonstrate shelving of a circuit atom, fluxonium, placed inside a microwave waveguide. With no cavity modes in the setup, the qubit coherence time exceeds 50 μs, and the cycling transition’s radiative lifetime is under 100 ns. By detecting a homodyne fluorescence signal from the cycling transition, we implement a QND readout of the qubit and account for readout errors using a minimal optical pumping model. Our result establishes a resource-efficient (cavityless) alternative to cQED for controlling superconducting qubits.

Ultranarrow spectral line of the radiation in double qubit-cavity ultrastrong coupling system.

The ultrastrongly coupling (USC) system has very important research significance in quantum simulation and quantum computing. In this paper, the ultranarrow spectrum of a circuit QED system with two qubits ultrastrongly coupled to a single-mode cavity is studied. In the regime of USC, the JC model breaks down and the counter-rotating terms in the quantum Rabi Hamiltonian leads to the level anti-crossing in the energy spectrum. Choosing a single-photon driving field at the point of avoided-level crossing, we can get an equivalent four-level dressed state model, in which the dissipation of the two intermediate states is only related to the qubits decay. Due to the electron shelving of these two metastable states, a narrow peak appears in the cavity emission spectrum. Furthermore, we find that the physical origin for the spectral narrowing is the vacuum-induced quantum interference between two transition pathways. And this interference effect couples the slowly decaying incoherent components of the density matrix into the equations of the sidebands. This result provides a possibility for the study of quantum interference effect in the USC system.

Quantum Zeno effect by incomplete measurements

A measurement process needs a time duration in many actual cases, such as the measurement on atomic system by the electron shelving technique. If this timescale is deficient, the measurement would be incomplete. Here, we investigate the quantum Zeno effect by incomplete measurements. We show that an efficient freeze of the quantum state by incomplete measurements is available. And interestingly, this state freeze can be more significant than that obtained in the complete measurement case if the parameters of incomplete measurements are properly set.

Demonstration of quantum anti-Zeno effect with a single trapped ion**Project supported by the National Basic Research Program of China (Grant No. 2016YFA0301903), the National Natural Science Foundation of China (Grant Nos. 11174370, 11304387, 61632021, 11305262, 11574398, and N 61205108), and the Research Plan Project of National University of Defense Technology, China (Grant No. ZK16-03-04).

We experimentally demonstrate the quantum anti-Zeno effect in a two-level system based on a single trapped ion 40Ca+. In the large detuning regime, we show that the transfer from the ground state to the excited state can be remarkably enhanced by the inserted projection measurements. The inserted measurements in our experiment are realized by the electron shelving technique. Compared to the ideal projection measurement, which makes the quantum state collapse instantaneously, a practical electron shelving process needs a finite time duration. The minimum time for this collapse process is shown to be inversely proportional to the square of the coupling strength between the measurement laser and the system.

Time-dependent spectra of a three-level atom in the presence of electron shelving

We investigate time-dependent spectra of the intermittent resonance fluorescence of a single, laser-driven, three-level atom due to electron shelving. After a quasi-stationary state of the strong transition, a slow decay due to shelving leads to the steady state of the three-level system. The long-term stationary spectrum consists of a coherent peak, an incoherent Mollow-like structure, and a very narrow incoherent peak at the laser frequency. We find that in the ensemble average dynamics the narrow peak emerges during the slow decay regime, after the Mollow spectrum has stabilized, but well before an average dark time has passed. The coherent peak, being a steady state feature, is absent during the time evolution of the spectrum

Phase-dependent fluctuations of intermittent resonance fluorescence

Electron shelving gives rise to bright and dark periods in the resonance fluorescence of a three-level atom. The corresponding incoherent spectrum contains a very narrow inelastic peak on top of a two-level-like spectrum. Using the theories of balanced and conditional homodyne detection we study ensemble averaged phase-dependent fluctuations of intermittent resonance fluorescence. The sharp peak is found only in the spectra of the squeezed quadrature. In balanced homodyne detection that peak is positive, which greatly reduces the squeezing, also seen in its variance. In conditional homodyne detectionCHD, for weak to moderate laser intensity, the peak is negative, enhancing the squeezing, and for strong fields the sidebands become dispersive which, together with the positive sharp peak dominate the spectrum. The latter effect is due to non-negligible third order fluctuations produced by the atom-laser nonlinearity and the increased steady state population of the shelving state. A simple mathematical approach allows us to obtain accurate analytical results.

Precision Isotope Shift Measurements in Calcium Ions Using Quantum Logic Detection Schemes.

We demonstrate an efficient high-precision optical spectroscopy technique for single trapped ions with nonclosed transitions. In a double-shelving technique, the absorption of a single photon is first amplified to several phonons of a normal motional mode shared with a cotrapped cooling ion of a different species, before being further amplified to thousands of fluorescence photons emitted by the cooling ion using the standard electron shelving technique. We employ this extension of the photon recoil spectroscopy technique to perform the first high precision absolute frequency measurement of the 2D(3/2)→2P(1/2) transition in calcium, resulting in a transition frequency of f=346 000 234 867(96) kHz. Furthermore, we determine the isotope shift of this transition and the 2S(1/2)→2P(1/2) transition for 42Ca+, 44Ca+, and 48Ca+ ions relative to 40Ca+ with an accuracy below 100 kHz. Improved field and mass shift constants of these transitions as well as changes in mean square nuclear charge radii are extracted from this high resolution data.

Circuit-QED-based scalable architectures for quantum information processing with superconducting qubits

We discuss different ways of generating entanglement in the original picture of circuit QED (XcQED) and several restrictions that arise in the context of a large-scale quantum architecture. To alleviate some of the issues posed by the presence of the nonlinearities inherent to these systems, we introduce a layout for circuit QED, wherein an artificial atom is coupled to a quantized radiation field via its longitudinal degree of freedom (ZcQED). This system is akin to ion traps used in atomic physics, but it relies on fixed coupling between the atom and the resonator. We describe a scalable architecture for processing quantum information with superconducting qubits, which is free from any type of residual interaction between the atomic and photonic degrees of freedom. Tunable interactions can be realized based on sideband transitions, and the system can be operated out of the Lamb-Dicke regime, allowing it to benefit from the possibility of achieving large coupling strengths between atoms and resonators. We also discuss a readout scheme that does not require any extra circuits and allows a qubit-specific measurement of the state of the quantum register inspired by the electron shelving technique. This scheme is quantum nondemolition (QND)-like, and allows for single-shot determination of the qubit states.

Early observations of macroscopic quantum jumps in single atoms

The observation of intermittent fluorescence of a single atomic ion, a phenomenon better known as ‘macroscopic quantum jumps,’ was an important early scientific application of the three-dimensional rf quadrupole (Paul) trap. The prediction of the phenomenon by Cook and Kimble grew out of a proposal by Dehmelt for a sensitive optical double-resonance technique, called ‘electron shelving.’ The existence of the quantum jumps was viewed with skepticism by some in the quantum optics community, perhaps due to the failure of some conventional calculations, for example the solutions to the optical Bloch equations, to predict them. Quantum jumps were observed nearly simultaneously by three different experimental groups, all with single, isolated ions in Paul traps. Some slightly earlier observations of excessive fluctuations in the laser-induced fluorescence of a single Hg+ ion by a group at the National Institute of Standards and Technology, viewed in retrospect, were due to quantum jumps. Similarly, sudden changes in the resonance fluorescence of trapped Ba+ ions observed by a group at the University of Hamburg were due to quantum jumps, although this was not understood at first. This shows how discoveries can be missed if unanticipated observations are ignored rather than investigated. A fourth experiment, performed not with a single, trapped ion, but with neutral atoms transiently observed in an atomic beam, and published at about the same time as the other experiments, has been almost totally neglected.

Magnetically induced electron shelving in a trapped Ca+ion

Atomic states are perturbed by externally applied magnetic fields (Zeeman effect). As well as the usual Zeeman splittings, the magnetic field leads to mixing of states with different values of the $J$ quantum number. We report on the direct experimental measurement of this effect using the electron shelving technique (employed to great effect in single-ion spectroscopy and quantum-information processing). Specifically we observe shelving to the metastable ($3{p}^{6}3d$) ${}^{2}{D}_{5/2}$ state in a single $^{40}\mathrm{Ca}$${}^{+}$ ion, via spontaneous decay on the strongly forbidden $4p {}^{2}{P}_{1/2}\ensuremath{\leftrightarrow}3d {}^{2}{D}_{5/2}$ transition. The rate of this transition is shown to scale as the square of the magnetic-field strength. The scaling and magnitude of the effect is compared to the result derived from first-order perturbation theory. For applications in quantum-information processing the $J$-mixing effect causes a degradation of readout fidelity. We show that this degradation is at a tolerable level for Ca${}^{+}$ and is much less problematic for other trapped ionic species.

Optical spectroscopy of rubidium Rydberg atoms with a 297 nm frequency-doubled dye laser

We demonstrate Doppler-free, purely optical detection of laser-excited rubidium Rydberg atoms in a room-temperature gas cell. The Rydberg atoms are excited with a frequency-doubled dye laser at 297 nm in a single-excitation step from the ground state; the detection is performed with a 780 nm diode laser in a scheme similar to electron shelving. Laser spectroscopy of Rydberg transitions is demonstrated, and a frequency-doubled dye is stabilized to one Rydberg transition in the UV. The performance of this stabilization is measured with an atomic-beam apparatus and a time of flight experiment.

Atomic cluster state build-up with macroscopic heralding

We describe a measurement-based state preparation scheme for the efficient build-up of cluster states in atom-cavity systems. As in a recent proposal for the generation of maximally entangled atom pairs [Metz et al., Phys. Rev. Lett. 97, 040503 (2006)], we use an electron shelving technique to avoid the necessity for the detection of single photons. Instead, the successful fusion of smaller into larger clusters is heralded by an easy-to-detect macroscopic fluorescence signal. High fidelities are achieved even in the vicinity of the bad cavity limit and are essentially independent of the concrete size of the system parameters.

ELECTRON SHELVING INDUCED SQUEEZING IN FLUORESCENT LIGHT EMITTED BY COLD 4He ATOMS IN AN OPTICAL LATTICE: COHERENT CONTROL BY A WEAK AXIAL MAGNETIC FIELD

We report theoretical calculations on the effect of polarization gradient, atomic motion and an axial magnetic field on quantum noise reduction in the resonant fluorescence emitted by a cloud of cold Helium atoms in an optical lattice. The polarization gradient induces squeezing of the electromagnetic field at selected points on the optical lattice, together with a dark resonance in the emitted fluorescence, the origin of which is traced back to electron shelving. We find that the localization of the atoms in the optical lattice destroys squeezing, but can be recovered in the presence of an axial magnetic field.

Polarization gradient induced electron shelving in cold helium atoms in an optical lattice: effect of axial magnetic field

We report the effect of atomic motion and an axial magnetic field on the spectrum of resonance fluorescence emitted by cold helium atoms in an optical lattice. The polarization gradient induces electron shelving at selected points on the optical lattice, giving rise to light and dark periods. We find in particular that localization of the atoms in the optical lattice inhibits electron shelving but can be recovered in the presence of an axial magnetic field.

Quantum stochastic resonance in electron shelving

Stochastic resonance shows that under some circumstances noise can enhance the response of a system to a periodic force. While this effect has been extensively investigated theoretically and demonstrated experimentally in classical systems, there is complete lack of experimental evidence within the purely quantum-mechanical domain. Here we demonstrate that stochastic resonance can be exhibited in a single ion and would be experimentally observable using well mastered experimental techniques. We discuss the use of this scheme for the detection of the frequency difference of two lasers to demonstrate that stochastic resonance may have applications in precision measurements at the quantum limit.

Resonance fluorescence spectrum of a trapped ion undergoing quantum jumps

We experimentally investigate the resonance fluorescence spectrum of single 171Yb and 172Yb ions which are laser cooled to the Lamb-Dicke regime in a radiofrequency trap. While the fluorescence scattering of 172Yb is continuous, the 171Yb fluorescence is interrupted by quantum jumps because a nonvanishing rate of spontaneous transitions leads to electron shelving in the metastable hyperfine sublevel 2D3/2(F=2). The average duration of the resulting dark periods can be varied by changing the intensity of a repumping laser field. Optical heterodyne detection is employed to analyze the fluorescence spectrum near the Rayleigh elastic scattering peak. It is found that the stochastic modulation of the fluorescence emission by quantum jumps gives rise to a Lorentzian component in the fluorescence spectrum, and that the linewidth of this component varies according to the average duration of the dark fluorescence periods. The experimental observations are in quantitative agreement with theoretical predictions.

Cooperative effects in the light and dark periods of two dipole-interacting atoms

If an atom is able to exhibit macroscopic dark periods, or electron shelving, then a driven system of two atoms has three types of fluorescence periods (dark, single, and double intensity). We propose to use the average durations of these fluorescence types as a simple and easily accessible indicator of cooperative effects. As an example, we study two dipole-interacting V systems by simulation techniques. We show that the durations of the two types of light periods exhibit marked separation-dependent oscillations and that they vary in phase with the real part of the dipole-dipole coupling constant.

Narrow absorption lines induced by electron shelving

We investigate the absorption spectrum of a laser-driven V system in which one of the upper levels is metastable. If the Rabi frequency of the laser driving the metastable transition is sufficiently small we find an extremely narrow peak in the stationary absorption spectrum of a weak probe on the strong transition. We give analytical expressions approximating the stationary absorption spectrum. The absorption spectrum of a two-level system is investigated for the case where an upper limit for the time separation of successive emissions is given. The absorption spectrum then exhibits a delta-function-like peak and using this we then show that the origin of the narrow peak in the absorption spectrum can be traced back to electron shelving, i.e. to the existence of light and dark periods in the resonance fluorescence emitted on the strong transition.