Spontaneous Channels Research Articles

Two-dimensional atom localization via spontaneous emission in a coherently driven five-level M-type atomic system

A scheme is proposed for two-dimensional atom localization in the subwavelength domain via controlled spontaneous emission. We consider a five-level M-type atomic system interacting with two orthogonal standing-wave laser fields and the vacuum of the radiation field. The interaction of the atom with space-dependent standing-wave fields can provide information about the position of the atom passing through, thus leading to atom localization. It is found that the localization is significantly improved due to the interference effect between the spontaneous decay channels and the dynamically induced quantum interference generated by the two standing-wave fields. By properly varying the system parameters, we can achieve high-precision and high-resolution atom localization.

Two-dimensional atom localization via controlled spontaneous emission from a driven tripod system

A scheme for two-dimensional (2D) subwavelength atom localization is proposed, in which the atom is in a four-level tripod configuration and driven by two orthogonal standing-wave lasers. Because of the spatial dependence of atom-field interaction, the spontaneously emitted photon carries information about the position of the atom in standing-wave fields. We exploit this fact to 2D atom localization conditioned on the measurement of spontaneously emitted photon at a particular frequency, and obtain a high precision and resolution in the position probability distribution. Moreover, an improvement by a factor of 2 in the detecting probability of an atom can be achieved by initially preparing the atom in the coherent population trapping state. Qualitatively, the high-precision, high-resolution atom localization can be attributed to the quantum interference effect between competitive multiple spontaneous decay channels.

The Kerr Nonlinearity in an N-Type Four-Level System via Spontaneously Generated Coherence

The Kerr nonlinearity is investigated in an N-type four-level atomic system whose both supper levels are degenerated or nearly degenerate. It is found that the spontaneously generated coherence as a result of the degenerate levels can change the Kerr nonlinearity dramatically depending on the angle between two spontaneous channels. In addition, we discover that the probe field makes its own contribution to the nonlinearity in comparison to indifference in general three-level systems.

Schemes for the generation of multipartite entanglement of remote atoms trapped in separate optical cavities

Based on the interference effect of polarized photons leaking out of separate cavities, we propose schemes for the generation of the N-atom Greenberger–Horne–Zeilinger (GHZ) state, three-atom W state and a genuine four-atom entangled state |χ⟩. In these schemes, each of the atoms is trapped separately in a remote optical cavity, and the possible spontaneous channels induced by the excited atoms lead to the coherent superposition of the states of the atoms. The desired multipartite entangled states can be generated with a certain success probability by the subsequent detection of the polarized photons in different modes. The schemes would be useful steps towards long-distance quantum communication, distributed quantum computation and constructing remote quantum information processing networks.

Plasmon-Induced Enhancement of Quantum Interference near Metallic Nanostructures

We show that the quantum interference between two spontaneous emission channels can be greatly enhanced when a three-level V-type atom is placed near plasmonic nanostructures such as metallic slabs, nanospheres, or periodic arrays of metal-coated spheres. The spontaneous emission rate is calculated by a rigorous first-principles electromagnetic Green's tensor technique. The enhancement of quantum interference is attributed to the strong dependence of the spontaneous emission rate on the orientation of an atomic dipole relative to the surface of the nanostructure at the excitation frequencies of surface plasmons.

Caffeine inhibits nonselective cationic currents in interstitial cells of Cajal from the murine jejunum

Interstitial cells of Cajal (ICC) discharge unitary potentials in gastrointestinal muscles that constitute the basis for pacemaker activity. Caffeine has been used to block unitary potentials, but the ionic conductance responsible for unitary potentials is controversial. We investigated currents in cultured ICC from murine jejunum that may underlie unitary potentials and studied the effects of caffeine. Networks of ICC generated slow wave events under current clamp, and these events were blocked by caffeine in a concentration-dependent manner. Single ICC generated spontaneous transient inward currents (STICs) under voltage clamp at -60 mV and noisy voltage fluctuations in current clamp. STICs were unaffected when the equilibrium potential for Cl- (ECl) was set to -60 mV (excluding Cl- currents) and reversed at 0 mV, demonstrating that a nonselective cationic conductance, and not a Cl- conductance, is responsible for STICs in ICC. Caffeine inhibited STICs in a concentration-dependent manner. Reduced intracellular Ca2+ and calmidazolium (CMZ; 1 microM) activated persistent inward, nonselective cation currents in ICC. Currents activated by CMZ and by dialysis of cells with 10 mM BAPTA were also inhibited by caffeine. Excised inside-out patches contained channels that exhibited spontaneous openings, and resulting currents reversed at 0 mV. Channel openings were increased by reducing Ca2+ concentration from 10(-6) M to 10(-8) M. CMZ (1 microM) also increased openings of nonselective cation channels. Spontaneous currents and channels activated by CMZ were inhibited by caffeine (5 mM). The findings demonstrate that the Ca2+-inhibited nonselective cation channels that generate STICs in ICC are blocked directly by caffeine. STICs are responsible for unitary potentials in intact muscles, and the block of these events by caffeine is consistent with the idea that a nonselective cation conductance underlies unitary potentials in ICC.

WAVELENGTH CONVERSION OF MULTICHANNEL SPECTRUM-SLICED ASE SIGNALS VIA FOUR-WAVE MIXING IN HIGHLY NONLINEAR DISPERSION-SHIFTED FIBER

Simultaneous wavelength conversion of multiple spectrum-sliced amplified spontaneous emission channels is achieved experimentally via four-wave mixing (FWM) in highly-nonlinear dispersion-shifted fiber. A theoretical model for FWM between coherent pump and incoherent signals is built based on FWM theory of coherent light. The theoretical result agrees well with the experimental result.

Quantum interference effect on spontaneous emission spectrum in a doubly driven M-type atom

An M-type atomic system with two closely spaced upper levels interacting with the same modes of the vacuum radiation field exhibits the interference effect between the spontaneous decay channels. The phenomenon of this decay-interference along with the dynamically induced quantum interference created in the system by two coherent fields can change significantly the spontaneous emission spectrum. Our results highlight large enhancement of ultranarrow spectral components within the spontaneous emission line shape in various conditions. We have shown the occurrence of two contradistinctive phenomena: compression of two spectral lines towards their mid-position and the spreading of two lines away from each other under different dynamic conditions. The phenomenon of suppression of spectral line and the quenching of spontaneous emission have also been focused.

Vacuum induced interference effect in probe absorption in a driven Y-type atom

We have analyzed the properties of weak probe absorption in a closed four-level Y-type system driven by a coherent driving field. The system with two nearly degenerate uppermost levels interacting with the same modes of the vacuum radiation field exhibits the interference effect between the spontaneous decay channels. The phenomenon of this quantum interference can significantly change the absorptive response of the weak probe field. On varying the amplitude of the resonant driving field, in the absence of incoherent pumping in the upper transitions the system can display probe transparency as well as enhanced absorption peak under the condition of resonant detuning of the probe field. With the application of incoherent pumping to the system the phenomenon of symmetric light amplification with two distinct gain peaks one each at the positions of Autler–Townes resonances can be achieved in the presence of the decay-interference effect. We have also shown that the unidirectional incoherent pumping mode is necessary for the evolution of probe gain.

Transparency and spontaneous emission in a densely doped photonic band gap material

The susceptibility has been calculated for a photonic crystal in the presence of spontaneous cancellation and dipole–dipole interaction. The crystal is densely doped with an ensemble of four-level nano-particles in Y-type configuration. Probe and a pump laser fields are applied to manipulate the absorption coefficient of the system. The expression of the susceptibility has been calculated in the linear response regime of the probe field but nonlinear terms are included for the pump field. It is found that in the presence of spontaneous emission cancellation there is an increase in the height of the two absorption peaks however the phenomenon of electromagnetically induced transparency (EIT) is not affected. On the other hand, there is a change in the height and location of the two peaks in the presence of dipole–dipole interactions. For certain values the particle density of the system can be switched from the EIT state to the non-EIT state. It is also found that when the resonance energies for two spontaneous emission channels lie close to the band edge, the EIT phenomenon disappears.

Comment on “Interference-induced gain in the Autler-Townes doublet of a V-type atom in a cavity” and “Cavity implementation of quantum interference in a Λ-type atom”

In a couple of papers [Phys. Rev. A, 63, 033818 (2001); 63, 023810 (2001)], P. Zhou, S. Swain, and L. You studied the cavity-induced modifications to the Autler-Townes spectrum of three-level atoms due to the phenomenon of quantum interference. They demonstrated that probe gain can occur in either of the Autler-Townes doublet due to the cavity-induced interference among spontaneous decay channels. In this Comment, we show that this conclusion is incorrect and it contradicts the thermodynamic equilibrium conditions of the atomic system in steady state.

Large index of refraction without absorption via decay-induced coherence in a three-level V system

We study the effects of quantum interference from spontaneous emission on the dispersion-absorption properties in a three-level V-type atomic system with two near-degenerate excited levels. We found that due to the quantum interference between two spontaneous decay channels, large index of refraction without absorption always can be obtained just by choosing proper values of the relative phase between the two applied fields.

Effect of vacuum-induced coherence on single- and two-photon absorption in a four-level Y-type atomic system

When a four-level Y-type atom with two highest nearly degenerate lying levels interacts with the same vacuum radiation field, its excited levels have vacuum-induced coherence due to the quantum interference between the spontaneous decay channels. We consider the effects of the vacuum-induced coherence on the electromagnetically induced transparency against single- and two-photon absorption in the atomic system. We find that the vacuum-induced coherence can lead to probe gain without incoherent pumping. On the other hand, the coherence can suppress the two-photon transparency, even in some cases where it can enhance the two-photon absorption. Another important result is the finding of the crucial role played by the relative phase between the probe and coupling fields: the two-photon transparency and the probe gain spectra can be modulated by this phase.

Enhancement of steady-state squeezing in the resonance fluorescence of a coherently driven four-level atom ofΛconfiguration via quantum interference

We investigate steady-state squeezing in the phase quadratures of the resonance fluorescence emitted from a coherently driven four-level atom of {lambda} configuration. Quantum fluctuation spectra of the optimum-phase quadratures are calculated. We show that if quantum interference between spontaneous emission channels from closed excited states to lower levels of the atom takes place, squeezing in the optimum-phase quadrature can occur in a very wider region of the parameter space than that predicted by previous studies. We also show that the quantum interference can greatly change the atomic coherences and then lead to this interesting result.

Entangling distant atoms by interference of polarized photons.

We propose a scheme to generate the entangled state of two Lambda-type three-level atoms trapped in distant cavities by using interference of polarized photons. Two possible spontaneous emission channels of each excited atom result in a coherent superposition of the states of two atoms. The subsequent detection of the different polarized photons reveals that both atoms are in different ground states, but an interference effect prevents us from distinguishing which atom is in which ground state; the atoms are thus entangled. In comparison with the original proposal of interference-induced entanglement [C. Cabrillo, J. Cirac, P. Garcia-Fernandez, and P. Zoller, Phys. Rev. A 59, 1025 (1999)]], in our scheme the weakly driven condition is not required, and the influence of atomic excitement and atomic recoil on the entanglement fidelity can be eliminated.

Transient response in a three-level V system with spontaneously generated coherence

In a V-type three-level atomic system with two near-degenerate excited levels, due to interaction with the vacuum of the radiation field, there exists a kind of quantum interference between two spontaneous decay channels, spontaneously generated coherence. In this paper, we investigate the effects of this kind of coherence on the transient process in the presence of a weak probe and a strong coherent field. We find that the properties of the transient process can be dramatically affected by the spontaneously generated coherence. The transient gain can be greatly enhanced due to the quantum interference from spontaneous emission, and the transient absorption can be almost eliminated just by choosing the proper relative phase between the two fields.

Response of the probe gain with or without inversion to the relative phase of two coherent fields in a three-level V model

We investigate a V-type three-level atomic system with two near-degenerate excited levels, which is driven by a strong coherent field and a weak probe field. We find that, due to the quantum interference between two spontaneous decay channels, even in the absence of an incoherent pumping, the probe gain can be achieved and modulated at different probe detunings just by tuning the relative phase between the probe and the coherent field to different regions. By demonstrating the gain-absorption coefficient as well as the population difference on the probe transition, we show that the probe gain can be either with or without population inversion, which depends on detunings, spontaneous decay rates, and the relative phase. In this atomic system, the phase-dependent probe gain originates from the internal quantum interference effect as well as the external dynamically induced coherence effect.

Do clinical and angiographic parameters predict failure of medical therapy in patients suitable for coronary angioplasty?

Aims: Recent studies have suggested that patients with coronary disease suitable for angioplasty have an equally good outcome with medical therapy if clinically stable. Complex lesion morphology may predict acute events without intervention and stenosis severity influences the degree of collateralisation. This study was designed to assess the influence of these factors on clinical outcome. Methods and results: A retrospective review of patients suitable for angioplasty who were randomised to initial medical therapy as part of a multicentre study. Angiograms were reviewed for lesion characteristics, TIMI flow grade, and degree of collateralisation. Angiograms were available on 79 patients (13 female, 66 male). Mean age was 54.8 years (range 43–68) in the group crossing-over to revascularisation, and 58.4 (range 37–78) in the group who did not ( P=ns). Seventeen patients crossed-over (two to CABG, 15 to PTCA) at 5.4 months (range 0–10) after initial angiography. Disease progression had occurred in 10/17 patients (58.8%), three of whom developed a new occlusion. Collateralisation was more likely in smokers, independent of lesion severity ( P<0.05). Time to cross-over was not influenced by progression of disease. Crossing-over was not affected by age, diabetic status, cholesterol level, vessel involved, lesion severity, TIMI flow, lesion morphology, collateralisation, or the number of vessels diseased, but was more likely in females ( P<0.05). Conclusion: This group of patients generally does well with medical therapy. Whilst the numbers are relatively small, there does not appear to be any reliable prospective marker, including the presence of spontaneous collateral channels on diagnostic angiography, to indicate which patients will fail medical therapy and require revascularisation.

The effect of external divalent cations on spontaneous non-selective cation channel currents in rabbit portal vein myocytes.

1. The effects of external divalent cations on spontaneous single non-selective cation channel currents were studied in outside-out patches from rabbit portal vein smooth muscle cells in K+-free conditions. 2. In an external medium containing 1.5 mM Ca2+ (Ca2+o) the majority of spontaneous channel currents had a unitary conductance of 23 pS, reversal potential (Vr) of +10 mV and a low open probability (Po) at negative patch potentials. Some channels opened to a lower conductance state of about 13 pS suggesting that the cation channels have two conductance states. Open time and burst duration distributions could both be described by two exponentials with time constants of about of 1 ms and 7 ms for open times and 3 ms and 16 ms for burst durations. 3. In 0 Ca2+o the majority of spontaneous cation channels had a unitary conductance of 13 pS and Vr was shifted to +4 mV. Moreover the longer open time and longer burst duration time constants were both reduced to approximately half the values in 1.5 mM Ca2+o. 4. Compared to 0 Ca2+o the single channel currents in 3 microM and 100 microM Ca2+o had a 5- to 6-fold increase in Po which was accompanied by increases in both open times and burst durations. In 3 microM and 100 microM Ca2+o the unitary conductance of the single channel currents was between 22 and 26 pS. 5. At positive membrane potentials the single channel currents had an increased Po compared to negative potentials which was associated with increased open times and burst durations but these values were similar in 3 microM, 100 microM and 1.5 mM Ca2+o. 6. In 1.5 mM Sr2+o and 1.5 mM Ba2+o channels opened to the higher conductance state of about 22-25 pS and had a 3- to 7-fold greater Po than in 0 Ca2+o. 7. In conclusion, external divalent cations have marked effects on the unitary conductance and kinetic behaviour of non-selective cation channels in rabbit portal vein smooth muscle cells.

Comparison of spontaneous and noradrenaline-evoked non-selective cation channels in rabbit portal vein myocytes.

The properties of non-selective cation channels were studied in rabbit portal vein smooth muscle cells in K+-free conditions with patch pipette techniques. In about 45 % of isolated outside-out patches spontaneous channel currents with a unitary conductance of 23 pS were observed. The reversal potential was +11 mV which was shifted to more negative values and the unitary conductance was reduced when part of the external Na+ was replaced by Tris. At negative potentials the probability of opening (Po) was low and the open time distributions were described by two exponentials with time constants of about 1 and 7 ms. At positive potentials Po and the longer mean open time were greatly increased. The channel exhibited bursting behaviour and the burst duration distributions were described by two exponentials with time constants of about 3 and 15 ms. At positive potentials the longer burst duration was increased substantially. Application of noradrenaline and the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) to the external membrane of quiescent patches evoked single-channel activity with a unitary conductance of about 23 pS and with similar kinetic behaviour to that of the spontaneous channel currents. In conclusion, noradrenaline and OAG activate non-selective cation channel currents in excised patches of rabbit portal vein myocytes with a unitary conductance and kinetic properties that are similar to those of spontaneous channel currents. These channels have two open states and exhibit bursting behaviour. It is suggested that these channels underlie the whole-cell currents evoked by noradrenaline and OAG.