arXiv subjects

Adriana Pálffy

Publications and source records attributed to Adriana Pálffy.

At least 55 records · Page 3Linked to original sources

arXiv2019

Collective effects in $^{229}$Th-doped crystals

Vacuum-ultraviolet-transparent crystals have been proposed as host lattice for the coherent driving of the unusually low-lying isomer excitation in $^{229}$Th for metrology and quantum optics applications. Here the possible collective effects occurring for the coherent pulse propagation in the crystal system are investigated theoretically. We consider the effect of possible doping sites, quantization axis orientation and pulse configurations on the scattered light intensity and signatures of nuclear excitation. Our results show that for narrow-pulse driving, the rather complicated quadrupole splitting of the level scheme is significantly simplified. Furthermore, we investigate complex driving schemes with a combination of pulsed fields and investigate the occurring interference process. Our theoretical results support experimental attempts for first direct driving of the nuclear transition with coherent light.

physics.atom-ph↗

arXiv2018

Theoretical predictions for the magnetic dipole moment of $^{229m}$Th

A recent laser spectroscopy experiment [J. Thielking et al., Nature (London) 556, 321 (2018)] has determined for the first time the magnetic dipole moment of the 7.8 eV isomeric state $^{229m}$Th. The measured value differs by a factor of approximately 5 from previous nuclear theory predictions based on the Nilsson model, raising questions about our understanding of the underlying nuclear structure. Here, we present a new theoretical prediction based on a nuclear model with coupled collective quadrupole-octupole and single-particle motions. Our calculations yield an isomer magnetic dipole moment of $μ_{ IS}= -0.35μ_N$ in surprisingly good agreement with the experimentally determined value of $-0.37(6)μ_N$, while overestimating the ground state dipole moment by a factor 1.4. The model provides further information on the states' parity mixing, the role and strength of the Coriolis mixing and the most probable value of the gyromagnetic ratio $g_R$ and its consequences for the transition probability $B(M1)$.

nucl-th↗

arXiv2018

X-ray-frequency modulation via periodic switching of an external magnetic field

Single x-ray photons can be resonantly scattered and stored with the help of suitable transitions in the atomic nucleus. Here, we investigate theoretically means of mechanical-free modulation for the frequency spectra of such x-ray photons via periodic switching of an external magnetic field. We show that periodically switching on and off an external magnetic field generating hyperfine splitting of the nuclear transition leads to the generation of equidistant narrow sidebands of the resonantly scattered response. This frequency-comb-like structure depends on the magnitude and orientation of the applied magnetic field and on the switching period. An analytical approach for the characterization of the comblike frequency spectrum is presented. The feasibility of the external control on the frequency modulation of the x-ray response is discussed in view of possible applications in high-resolution spectroscopy or quantum technology.

quant-ph↗

arXiv2018

Nuclear excitation by electron capture in optical-laser-generated plasmas

The process of nuclear excitation by electron capture in plasma environments generated by the interaction of ultra-strong optical lasers with solid-state samples is investigated theoretically. With the help of a plasma model we perform a comprehensive study of the optimal parameters for most efficient nuclear excitation and determine the corresponding laser setup requirements. We discern between the low-density plasma regime, modeled by scaling laws, and the high-density regime, for which we perform particle-in-cell calculations. As nuclear transition case study we consider the 4.85 keV nuclear excitation starting from the long-lived $^{93\mathrm{m}}$Mo isomer. Our results show that the optimal plasma and laser parameters are sensitive to the chosen observable and that measurable rates of nuclear excitation and isomer depletion of $^{93\mathrm{m}}$Mo should be already achievable at laser facilities existing today.

physics.plasm-ph↗

arXiv2018

The electric quadrupole channel of the 7.8 eV $~^{229}\mathrm{Th}$ transition

The unique isomeric transition at 7.8 eV in $~^{229}\mathrm{Th}$ has a magnetic dipole ($M1$) and an electric quadrupole ($E2$) multipole mixing. So far, the $E2$ component has been widely disregarded. Here, we investigate the nuclear physics nature and the impact of the $E2$ decay channel for the nuclear coupling to the atomic shell based on the newest theoretical predictions for the corresponding reduced nuclear transition probabilities. Our results show that the contribution of the $E2$ channel is dominant or at least of the same order of magnitude for internal conversion or electronic bridge transitions involving the atomic orbitals $7p$, $6d$ and $5f$. Notable exceptions are the internal conversion of the $7s$ electron and the electronic bridge between the electronic states $7s$ and $7p$, for which the $M1$ component dominates by two to three orders of magnitude. Caution is therefore advised when considering isomeric excitation or decay via nuclear coupling to the atomic shell, as the involved orbitals determine which multipole transition component dominates.

nucl-th↗

arXiv2018

Tailoring laser-generated plasmas for efficient nuclear excitation by electron capture

The optimal parameters for nuclear excitation by electron capture in plasma environments generated by the interaction of ultra-strong optical lasers with solid matter are investigated theoretically. As a case study we consider a 4.85 keV nuclear transition starting from the long-lived $^{93\mathrm{m}}$Mo isomer that can lead to the release of the stored 2.4 MeV excitation energy. We find that due to the complex plasma dynamics, the nuclear excitation rate and the actual number of excited nuclei do not reach their maximum at the same laser parameters. The nuclear excitation achievable with a high-power optical laser is up to twelve and up to six orders of magnitude larger than the values predicted for direct resonant and secondary plasma-mediated excitation at the x-ray free electron laser, respectively. Our results show that the experimental observation of the nuclear excitation of $^{93\mathrm{m}}$Mo and the subsequent release of stored energy should be possible at laser facilities available today.

physics.plasm-ph↗

arXiv2017

A laser excitation scheme for $^{229\text{m}}$Th

Direct laser excitation of the lowest known nuclear excited state in $^{229}$Th has been a longstanding objective. It is generally assumed that reaching this goal would require a considerably reduced uncertainty of the isomer's excitation energy compared to the presently adopted value of $(7.8\pm 0.5)$ eV. Here we present a direct laser excitation scheme for $^{229\text{m}}$Th, which circumvents this requirement. The proposed excitation scheme makes use of already existing laser technology and therefore paves the way for nuclear laser spectroscopy. In this concept, the recently experimentally observed internal-conversion decay channel of the isomeric state is used for probing the isomeric population. A signal-to-background ratio of better than $10^4$ and a total measurement time of less than three days for laser scanning appear to be achievable.

nucl-ex↗

arXiv2017

Laser-induced electronic bridge for characterization of the $~^{229\rm{m}}\rm{Th} \rightarrow ~^{229\rm{g}}\rm{Th}$ nuclear transition with a tunable optical laser

An alternative method to determine the excitation energy of the $~^{229\rm{m}}\rm{Th}$ isomer via the laser-induced electronic bridge is investigated theoretically. In the presence of an optical or ultra-violet laser at energies that fulfill a two-photon resonance condition, the excited nuclear state can decay by transfering its energy to the electronic shell. A bound electron is then promoted to an excited state by absorption of a laser photon and simultaneous de-excitation of the nucleus. We present calculated rates for the laser-induced electronic bridge process and discuss the experimental requirements for the corresponding setup. Our results show that depending on the actual value of the nuclear transition energy, the rate can be very high, with an enhancement factor compared to the radiative nuclear decay of up to $10^8$.

physics.atom-ph↗

arXiv2017

Optomechanically induced transparency of x-rays via optical control

The search for new control methods over light-matter interactions is one of the engines that advances fundamental physics and applied science alike. A specific class of light-matter interaction interfaces are setups coupling photons of distinct frequencies via matter. Such devices, nontrivial in design, could be endowed with multifunctional tasking. Here we envisage for the first time an optomechanical system that bridges optical and robust, high-frequency x-ray photons, which are otherwise notoriously difficult to control. The x-ray-optical system comprises of an optomechanical cavity and a movable microlever interacting with an optical laser and with x-rays via resonant nuclear scattering. We show that optomechanically induced transparency of a broad range of photons (10 eV-100 keV) is achievable in this setup, allowing to tune nuclear x-ray absorption spectra via optomechanical control. This paves ways for metrology applications, e.g., the detection of the $^{229}$Thorium clock transition, and an unprecedentedly precise control of x-rays using optical photons.

quant-ph↗

arXiv2017

Reduced transition probabilities for the gamma decay of the 7.8 eV isomer in $^{229}$Th

The reduced magnetic dipole and electric quadrupole transition probabilities for the radiative decay of the $^{229}$Th 7.8 eV isomer to the ground state are predicted within a detailed nuclear-structure model approach. We show that the presence and decay of this isomer can only be accounted for by the Coriolis mixing emerging from a remarkably fine interplay between the coherent quadrupole-octupole motion of the nuclear core and the single-nucleon motion within a reflection-asymmetric deformed potential. We find that the magnetic dipole transition probability which determines the radiative lifetime of the isomer is considerably smaller than presently estimated. The so-far disregarded electric quadrupole component may have non-negligible contributions to the internal conversion channel. These findings support new directions in the experimental search of the $^{229}$Th transition frequency for the development of a future nuclear frequency standard.

nucl-th↗

arXiv2017

Determination of plasma screening effects for thermonuclear reactions in laser-generated plasmas

Due to screening effects, nuclear reactions in astrophysical plasmas may behave differently than in the laboratory. The possibility to determine the magnitude of these screening effects in colliding laser-generated plasmas is investigated theoretically, having as a starting point a proposed experimental setup with two laser beams at the Extreme Light Infrastructure facility. A laser pulse interacting with a solid target produces a plasma through the Target Normal Sheath Acceleration scheme, and this rapidly streaming plasma (ion flow) impacts on a secondary plasma created by the interaction of a second laser pulse on a gas jet target. We model this scenario here and calculate the reaction events for the astrophysically relevant reaction $^{13}$C($^4$He, $n$)$^{16}$O. We find that it should be experimentally possible to determine the plasma screening enhancement factor for fusion reactions by detecting the difference in reaction events between two scenarios of ion flow interacting with the plasma target and a simple gas target. This provides a way to evaluate nuclear reaction cross-sections in stellar environments and can significantly advance the field of nuclear astrophysics.

physics.plasm-ph↗

arXiv2016

Internal conversion from excited electronic states of $^{229}{\mathrm Th}$ ions

The process of internal conversion from excited electronic states is investigated theoretically for the case of the vacuum-ultraviolet nuclear transition of $^{229}{\mathrm Th}$. Due to the very low transition energy, the $^{229}{\mathrm Th}$ nucleus offers the unique possibility to open the otherwise forbidden internal conversion nuclear decay channel for thorium ions via optical laser excitation of the electronic shell. We show that this feature can be exploited to investigate the isomeric state properties via observation of internal conversion from excited electronic configurations of ${\mathrm Th}^+$ and ${\mathrm Th}^{2+}$ ions. A possible experimental realization of the proposed scenario at the nuclear laser spectroscopy facility IGISOL in Jyväskylä, Finland is discussed.

physics.atom-ph↗

arXiv2016

Laser-Matter Interaction: Classical Regime versus Quantum Regime

Doppler backscattering of optical laser photons on a "flying mirror" of relativistic electrons promises to yield coherent photons with MeV-range energies. We compare the nuclear interaction of such a laser pulse with the standard atom-laser interaction. The mean-field description of atoms must be replaced by a rate equation and the classical field strength, far too faint in nuclei, by the dipole transition rate. Significant nuclear excitation occurs for photon numbers much smaller than typical for atoms. That drastically reduces the requirements on the experimental realization of a "flying mirror".

nucl-th↗

arXiv2016

An x-ray quantum eraser setup for time-energy complementarity

A new quantum eraser setup exploiting for the first time the time-energy complementarity relation in the x-ray regime is investigated theoretically. Starting point is the interference process between x-ray quanta driving two nuclear hyperfine transitions in a nuclear forward scattering setup. We show that which-way information can be obtained by marking the scattering paths with orthogonal polarization states, thus leading to the disappearance of the interference pattern. In turn, erasure of the which-way information leads to the reappearance of the interference fringes. We put forward two schemes using resonant scattering off nuclear targets and design which-way marking procedures to realize the quantum eraser setup for x-ray quanta.

quant-ph↗

arXiv2016

Collective magnetic splitting in single-photon superradiance

In an ensemble of identical atoms, cooperative effects like sub- or superradiance may alter the decay rates and the energy of specific transitions may be shifted from the single-atom value by the so-called collective Lamb shift. While such effects in ensembles of two-level systems are by now well understood, realistic multi-level systems are more difficult to handle. In this work we show that in a system of atoms or nuclei under the action of an external magnetic field, the collective contribution to the level shifts can amount to seizable deviations from the single-atom Zeeman or magnetic hyperfine splitting picture. We develop a formalism to describe single-photon superradiance in multi-level systems in the small sample limit and quantify the parameter regime for which the collective Lamb shift leads to measurable deviations in the magnetic-field-induced splitting. In particular, we show that this effect should be observable in the nuclear magnetic hyperfine splitting in Mössbauer nuclei embedded in thin-film x-ray cavities.

quant-ph↗

arXiv2016

Stopping narrow-band x-ray pulses in nuclear media

A control mechanism for stopping x-ray pulses in resonant nuclear media is investigated theoretically. We show that narrow-band x-ray pulses can be mapped and stored as nuclear coherence in a thin-film planar x-ray cavity with an embedded $^{57}\mathrm{Fe}$ nuclear layer. The pulse is nearly resonant to the 14.4 keV Mössbauer transition in the $^{57}\mathrm{Fe}$ nuclei. The role of the control field is played here by a hyperfine magnetic field which induces interference effects reminding of electromagnetically induced transparency. We show that by switching off the control magnetic field, a narrow-band x-ray pulse can be completely stored in the cavity for approximately 100 ns. Additional manipulation of the external magnetic field can lead to both group velocity and phase control of the pulse in the x-ray cavity sample.

quant-ph↗

arXiv2015

Laser-Nucleus Interactions: The Quasiadiabatic Regime

The interaction between nuclei and a strong zeptosecond laser pulse with coherent MeV photons is investigated theoretically. We provide a first semi-quantitative study of the quasiadiabatic regime where the photon absorption rate is comparable to the nuclear equilibration rate. In that regime, multiple photon absorption leads to the formation of a compound nucleus in the so-far unexplored regime of excitation energies several hundred MeV above the yrast line. The temporal dynamics of the process is investigated by means of a set of master equations that account for dipole absorption, stimulated dipole emission, neutron decay and induced fission in a chain of nuclei. That set is solved numerically by means of state-of-the-art matrix exponential methods also used in nuclear fuel burnup and radioactivity transport calculations. Our quantitative estimates predict the excitation path and range of nuclei reached by neutron decay and provide relevant information for the layout of future experiments.

nucl-th↗

arXiv2015

Direct and secondary nuclear excitation with x-ray free-electron lasers

The direct and secondary nuclear excitation produced by an x-ray free electron laser when interacting with a solid-state nuclear target is investigated theoretically. When driven at the resonance energy, the x-ray free electron laser can produce direct photoexcitation. However, the dominant process in that interaction is the photoelectric effect producing a cold and very dense plasma in which also secondary processes such as nuclear excitation by electron capture may occur. We develop a realistic theoretical model to quantify the temporal dynamics of the plasma and the magnitude of the secondary excitation therein. Numerical results show that depending on the nuclear transition energy and the temperature and charge states reached in the plasma, secondary nuclear excitation by electron capture may dominate the direct photoexcitation by several orders of magnitude, as it is the case for the 4.8 keV transition from the isomeric state of $^{93}$Mo, or it can be negligible, as it is the case for the 14.4 keV Mössbauer transition in $^{57}\mathrm{Fe}$. These findings are most relevant for future nuclear quantum optics experiments at x-ray free electron laser facilities.

physics.plasm-ph↗