Photon-ion Interaction Research Articles

Overview of recent CMS results

Recent results from the CMS Collaboration are presented. These measurements include a full physics program using ultraperipheral collisions such as photon-photon and photon-ion interactions, small collision systems including proton-proton and proton-lead collisions, and many measurements of hadronic ion-ion collisions. The properties of the quark-gluon plasma produced in ion-ion collisions are studied in detail. The measurements examine the number of degrees of freedom of the medium, the strength of jet quenching effects in the medium, the role of heavy flavor in hadronization processes, and more.

Persistent opto-ferroelectric responses in molecular ferroelectrics

Persistent photoresponses require optical excitations to metastable states, which are rare of ionic origin due to the indirect photon-ion interaction. In this work, we explore the photoinduced metastable proton states in the proton-transfer type molecular ferroelectric croconic acid. We observe that, after the photoexcitation, the changes of structural and ferroelectric properties relax in $\ensuremath{\sim}{10}^{3}\phantom{\rule{0.16em}{0ex}}\mathrm{s}$, indicating persistent photoresponses of ionic origin. In contrast, the photoconductivity relaxes within 1 s. The ${10}^{3}\phantom{\rule{0.28em}{0ex}}\mathrm{s}$ timescale suggests that the ionic metastable states result from proton transfer both along and out of the hydrogen bonds. This discovery unveils an ionic mechanism for the phototunability, which offers persistent opto-ferroelectric control for proton-transfer type molecular ferroelectrics.

Controlling rare-earth ions in a nanophotonic resonator using the ac Stark shift

On-chip nanophotonic cavities will advance quantum information science and measurement because they enable efficient interaction between photons and long-lived solid-state spins, such as those associated with rare-earth ions in crystals. The enhanced photon-ion interaction creates new opportunities for all-optical control using the ac Stark shift. Toward this end, we characterize the ac Stark interaction between off-resonant optical fields and Nd$^{3+}$-ion dopants in a photonic crystal resonator fabricated from yttrium orthovanadate (YVO$_4$). Using photon echo techniques, at a detuning of 160 MHz we measure a maximum ac Stark shift of 2$\pi\times$12.3 MHz per intra-cavity photon, which is large compared to both the homogeneous linewidth ($\Gamma_h =$100 kHz) and characteristic width of isolated spectral features created through optical pumping ($\Gamma_f \approx$3 MHz). The photon-ion interaction strength in the device is sufficiently large to control the frequency and phase of the ions for quantum information processing applications. In particular, we discuss and assess the use of the cavity enhanced ac Stark shift to realize all-optical quantum memory and detection protocols. Our results establish the ac Stark shift as a powerful added control in rare-earth ion quantum technologies.

Broadband biphoton generation and statistics of quantum light in the UV-visible range in an AlGaN microring resonator

We present a physical investigation on the generation of correlated photon pairs that are broadly spaced in the ultraviolet (UV) and visible spectrum on a AlGaN/AlN integrated photonic platform which is optically transparent at these wavelengths. Using spontaneous four wave mixing (SFWM) in an AlGaN microring resonator, we show design techniques to satisfy the phase matching condition between the optical pump, the signal, and idler photon pairs, a condition which is essential and is a key hurdle when operating at short wavelength due to the strong normal dispersion of the material. Such UV-visible photon pairs are quite beneficial for interaction with qubit ions that are mostly in this wavelength range, and will enable heralding the photon-ion interaction. As a target application example, we present the systematic AlGaN microresonator design for generating signal and idler photon pairs using a blue wavelength pump, while the signal appears at the transition of ytterbium ion (171Yb+, 369.5 nm) and the idler appears in the far blue or green range. The photon pairs have minimal crosstalk to the pump power due to their broad spacing in spectral wavelength, thereby relaxing the design of on-chip integrated filters for separating pump, signal and idler.

Resonance phenomena in collisions of atomic ions with electrons and photons

An overview is given on the physics of intermediate autoionizing states occurring in various observation channels of electron-ion and photon-ion interactions. Formation and decay processes of such resonances are numerous and involve intricate effects on the associated cross sections. Recent progress in the field has become possible by the combination of intense, high quality photon and electron beams with well prepared ionic targets. By using advanced ion source technology, storage ring capabilities and trapped ion techniques a wide spectrum of target species is accessible to studies of ionic resonances ranging from negative to highly charged positive ions and even to ions encapsulated within fullerene molecules.

Electron and laser interactions with positive ions

Recent progress in laboratory-based electron-ion scattering is reviewed, and the sensitivity of observed interference structure as a probe of collision dynamics is discussed. The extension of our use of positive ions as scattering targets to photon-ion interactions is demonstrated with the first ion-beam measurements for the fragmentation of a molecular ion, H-2(+), using intense femtosecond laser pulses.

Noise-induced fluctuations in two-ion systems driven by light beams

The dynamics of a system composed of two strongly coupled ions trapped in a time-dependent potential well and cooled by a laser beam is studied. In the present classical treatment the photon-ion interaction is simulated with an effective noise acting on the ions, which produces a stochastic transfer of momentum. The existence of noise-induced fluctuations in the regime where previous analysis indicated that the two-ion system dynamics was stable is discussed.

A stochastic approach to two-level ion dynamics driven by light beams

Abstract The probability distribution of a two-level ion confined in a harmonic trap and perturbed by the absorption and emission of photons is calculated. The ion is assumed to be excited by a light beam and relaxes back either by induced emissions or irreversible spontaneous emissions. The photon-ion interaction is modeled as a perturbing noise acting on the ion by modifying its energy and momentum. The current calculations reproduce the quantum results of the laser cooling of ions in static traps in the heavy particle limit.

Low noise asymptotic approach to the laser cooling of trapped ions

The probability distributions of dilute ion systems and two-ion systems trapped in time-dependent potential wells and driven by a radiation field are studied. Ions are excited by electromagnetic radiation and relax back due to either spontaneous or stimulated emissions. The photon statistics are considered Poissonian and the momentum transfer between the electromagnetic field, and the ions are assumed discrete. In the present classical treatment, the photon–ion interaction is simulated, with an effective noise acting on the ions, which produces a stochastic transfer of momentum. The present results are closely related to the quantum treatment in the heavy particle limit as well as to those derived from previous semiclassical models.

Multiphoton ionization–fragmentation patterns of tertiary amines

Multiphoton ionization (MPI)–fragmentation patterns are reported for a series of normal and caged tertiary amines. Ionization is enhanced by two-photon resonance with the 3s and 3p Rydberg states of trimethylamine, triethylamine, and the caged amines quinuclidine and triethylenediamine. Over the wavelength region λ = 400–530 nm, N(CH3)3 ionizes to the parent ion (P) and fragments only by the loss of a H atom to yield the P–H daughter ion; N(C2H5)3 ionizes to its parent ion and fragments by the loss of a methyl to form the P–CH3 ion. The branching ratio of daughter to parent ions is found to be essentially independent of laser intensity but strongly dependent on laser wavelength. The caged amines quinuclidine [N(C2H4)3CH, or ABCO] and triethylenediamine [N(C2H4)3N, or DABCO] fragment extensively over this λ range in a manner dependent on both laser wavelength and intensity. The extent of daughter ion formation in N(CH3)3 and N(C2H5)3 can be understood by consideration of the wavelength regions in which the total available energy from the initial three- or four-photon ionization event exceeds the appearance potential of the given daughter ion. For the caged amines direct observation of this mechanism is masked by fragmentation due to sequential absorption of photons (during the ∼5 ns pulse duration) by the parent and/or daughter ions. The present results show that even for molecules with broad, unstructured UV absorption and MPI spectra such as N(CH3)3 and N(C2H5)3, considerable information on photon–molecule and photon–ion interactions can still be gained by the MPI mass spectrometry technique.

Laser Spectroscopy of Negative Ion Beams

The availability of intense tunable and fixed frequency lasers has made it possible to investigate photon-ion interactions in crossed beam experiments. The short wavelength limitations of current lasers result in the greatest variety of applications having been made to studies of photon interactions with negative ions. Two major experimental approaches have been developed: fixed frequency laser negative ion photoelectron spectroscopy and tunable laser photode-tachment/photodissociation spectroscopy. The former approach is best suited for determination of electron affinities and structural properties of ions and free radicals, while the latter method provides highly accurate electron affinities and dynamical information on electron-molecule interactions. It is also possible to determine the internal energy content of negative ions. The experimental techniques and their limitations will be discussed in the form of several case studies: OH , C2 and the transition metals. Finally an attempt will be made to ascertain promising avenues for new investigations in this field.

Tandem quadrupole study of laser photodissociation of CO−3

Absolute cross sections for the production of O− by photodissociation of CO−3 have been determined at intervals of 1 nm or less throughout the range from 400 to 635 nm using a tandem quadrupole mass spectrometer equipped with a tunable dye laser. In addtion, the dependence of the apparent photodissociation cross section on ion source pressure, laser polarization, laser intensity, ion lens voltage, and pressure of CO2 in the photon–ion interaction region has been studied at selected wavelengths. The threshold for photodissociation of ground state CO−3 is found to be 2.258±0.008 eV in excellent agreement with a recent indirect determination of a lower limit for D(CO2–O−) of 2.27 eV, but in disagreement with earlier photodissociation results. Studies of collisional enhanced dissociation of laser excited ions indicate that only a fraction of the ions excited between threshold and 2.6 eV dissociate unimolecularly within 50 microsecond observation time. Below 2.2 eV, two photon dissociation of CO−3 is observed, and at 581 nm (2.13 eV) saturation of one of the transitions involved is observed, indicating a photoexcitation cross section of ca. 4×10−17 cm2. A model based on these observations is proposed which appears to account for the apparent disagreement between our results and earlier laser photodissociation work.