Femtosecond Covariance Spectroscopy to Control Multimode Quantum Correlations
Bulletin of the American Physical Society Go to link ❯
The vast majority of nonlinear optical spectroscopies work in an integrated mode, namely they use the mean-value signal, properly averaged over several stroboscopic repetitions. While ensuring an adequate signal-to-noise ratio, this approach relies strongly on pulse-to-pulse consistency and has thus motivated significant efforts in pursuit of perfect experimental stability. By contrast, we have developed a fundamentally different approach, named Femtosecond Covariance Spectroscopy (FCS), which identifies noise as a powerful and unique asset to access information that standard mean-value experiments miss. FCS is based on covariance rather than mean-value observables and relies on the study of multimode quantum correlations imprinted on stochastic ultrashort pulses by light-matter interactions. As a proof of principle, we have successfully applied such approach to the study of Raman-active vibrational modes excited through Impulsive Stimulated Raman Scattering (ISRS) in crystalline quartz. Nevertheless, the impact of FCS is not only limited to the field of condensed matter physics. Indeed, given the formal analogy between the quantum description of ISRS and optomechanical experiments, FCS could pave the way to a new generation of experiments in which the coupling between the electromagnetic field and the mechanical oscillator, could be reproduced by the interaction between light pulses and phonon modes.
Vibrational coherent control of localized d–d electronic excitation
A Marciniak, S Marcantoni, F Giusti, F Glerean, G Sparapassi, T Nova, A Cartella, S Latini, F Valiera, A Rubio, J van den Brink, F Benatti, D Fausti
Nature Physics volume 17, pages368–373(2021) Go to link ❯
Addressing the role of quantum coherence in the interplay between the different matter constituents (electrons, phonons and spin) is a critical step towards understanding transition metal oxides and designing complex materials with new functionalities. Here we use coherent vibrational control of on-site d–d electronic transitions in a model edge-sharing insulating transition metal oxide (CuGeO3) to single out the effects of vibrational coherence in electron-phonon coupling. By comparing time-domain experiments based on high- and low-photon-energy ultrashort laser excitation pulses with a fully quantum description of phonon-assisted absorption, we could distinguish the processes associated with incoherent thermal lattice fluctuations from those driven by the coherent motion of the atoms. In particular, while thermal fluctuations of the phonon bath uniformly increase the electronic absorption, the resonant excitation of phonon modes also results in light-induced transparency that is coherently controlled by the vibrational motion.
Anisotropic Time-Domain Electronic Response in Cuprates
F Giusti, A Montanaro, A Marciniak, F Randi, F Boschini, F Glerean, G Jarc, H Eisaki, M Greven, A Damascelli, A Avella, D Fausti
arXiv preprint arXiv:2012.11288, 2020 Go to link ❯
Superconductivity in the cuprates is characterized by spatial inhomogeneity and an anisotropic electronic gap of d-wave symmetry. The aim of this work is to understand how this anisotropy affects the non-equilibrium electronic response of high-Tc superconductors. We compare the nodal and antinodal non-equilibrium response to photo-excitation with photon energy comparable to the superconducting gap and polarization along the Cu-Cu axis of the sample. The data are supported by an effective d-wave BCS model indicating that the observed enhancement of the superconducting transient signal mostly involves an increase of pair coherence in the antinodal region, which is not induced at the node.
Signature of an Ultrafast Photo-Induced Lifshitz Transition in the Nodal-Line Semimetal ZrSiTe.
RJ Kirby, L Muechler, S Klemenz, C Weinberg, A Ferrenti, M Oudah, D Fausti, GD Scholes, LM Schoop
arXiv preprint arXiv:2011.04646, 2020 Go to link ❯
Here we report an ultrafast optical spectroscopic study of the nodal-line semimetal ZrSiTe. Our measurements reveal that converse to other compounds of the family, the sudden injection of electronic excitations results in a strongly coherent response of an A1g phonon mode which dynamically modifies the distance between Zr and Te atoms and Si layers.” Frozen phonon” DFT calculations, in which band structures are calculated as a function of nuclear position along the phonon mode coordinate, show that large displacements along this mode alter the material’s electronic structure significantly, forcing bands to approach and even cross the Fermi energy. The incoherent part of the time domain response reveals that a delayed electronic response at low fluence discontinuously evolves into an instantaneous one for excitation densities larger than 3.43×1017 cm−3 . This sudden change of the dissipative channels for electronic excitations is indicative of an ultrafast Lifshitz transition which we tentatively associate to a change in the topology of the Fermi surface driven by a symmetry preserving phonon mode.
Transient drude response dominates near-infrared pump–probe reflectivity in nodal-line semimetals ZrSiS and ZrSiSe.
RJ Kirby, A Ferrenti, C Weinberg, S Klemenz, M Oudah, S Lei, CP Weber, D Fausti, GD Scholes, LM Schoop
The journal of physical chemistry letters 11 (15), 6105-6111, 2020 Go to link ❯
The ultrafast optical response of nodal-line semimetals ZrSiS and ZrSiSe was studied in the near-infrared using transient reflectivity. The materials exhibit similar responses, characterized by two features, well-resolved in time and energy; the first decays after hundreds of femtoseconds, and the second lasts for nanoseconds. Using Drude–Lorentz fits of the materials’ equilibrium reflectance, we show that these are well-represented by a sudden change of the electronic properties (increase of screening or reduction of the plasma frequency) followed by an increase of the Drude scattering rate. This directly connects the transient data to a physical picture in which carriers, after excitation into the conduction band, return to the valence band by sharing excess energy with the phonon bath, resulting in a hot lattice that relaxes through slow diffusive processes. The emerging picture reveals that the sudden electronic reorganization instantaneously modifies the materials’ electronic properties on a time scale not compatible with electron–phonon thermalization.
Time-resolved multimode heterodyne detection for dissecting coherent states of matter.
F Glerean, G Jarc, A Marciniak, F Giusti, G Sparapassi, A Montanaro, E Maria Rigoni, J Owen Tollerud, D Fausti.
Optics Letters 45 (13), 3498-3501 2020 Go to link ❯
Unveiling and controlling the time evolution of the momentum and position of low energy excitations such as phonons, magnons, and electronic excitation is the key to attaining coherently driven new functionalities of materials. Here we report the implementation of femtosecond time- and frequency-resolved multimode heterodyne detection and show that it allows for independent measurement of the time evolution of the position and momentum of the atoms in coherent vibrational states in α-quartz. The time dependence of the probe field quadratures reveals that their amplitude is maximally changed when the atoms have maximum momentum, while their phase encodes different information and evolves proportionally to the instantaneous atomic position. We stress that this methodology, providing the mean to map both momentum and position in one optical observable, may be of relevance for both quantum information technologies and time-domain studies on complex materials.
Visible pump--mid infrared pump--broadband probe: development and characterization of a three-pulse setup for single-shot ultrafast spectroscopy at 50 kHz.
A Montanaro, F Giusti, M Colja, G Brajnik, A Marciniak, R Sergo, D De Angelis, F Glerean, G Sparapassi, G Jarc, S Carrato, G Cautero, D Fausti
arXiv preprint arXiv:2006.03442 2020 Go to link ❯
We report here an experimental setup to perform three-pulse pump-probe measurements over a wide wavelength and temperature range. By combining two pump pulses in the visible (650-900 nm) and mid-IR (5-20 μm) range, with a broadband supercontinuum white-light probe, our apparatus enables both the combined selective excitation of different material degrees of freedom and a full time-dependent reconstruction of the non-equilibrium dielectric function of the sample. We describe here the optical setup, the cryogenic sample environment and the custom-made acquisition electronics capable of referenced single-pulse detection of broadband spectra at the maximum repetition rate of 50 kHz, achieving a sensitivity of the order of 10−4 over an integration time of 1 s. We demonstrate the performance of the setup by reporting data on mid-IR pump, optical push and broadband probe in a single-crystal of Bi2 Sr2 Y0.08 Ca0.92 Cu2 O8+δ across the superconducting and pseudogap phases.
Vibrational coherent control of localized dd electronic excitation.
A Marciniak, S Marcantoni, F Giusti, F Glerean, G Sparapassi, T Nova, A Cartella, S Latini, F Valiera, A Rubio, J van den Brink, F Benatti, D Fausti
arXiv preprint arXiv:2003.13447 2020 Go to link ❯
Addressing the role of quantum coherence in the interplay between the different matter constituents (electrons, phonons and spin) is a critical step towards understanding transition metal oxides and design complex materials with new functionalities. Here we use coherent vibrational control of onsite dd electronic transitions in a model edge-sharing insulating transition metal oxide (CuGeO3) to single-out the effects of vibrational coherence in electron-phonon coupling. By comparing time domain experiments based on high and low frequency ultrashort pumps with a fully quantum description of phonon assisted absorption, we could distinguish the processes associated to incoherent thermal lattice fluctuations from those driven by the coherent motion of the atoms. In particular, while thermal fluctuation of the phonon bath uniformly increases the electronic absorption, the resonant excitation of phonon modes results also in light-induced transparency which is coherently controlled by the vibrational motion.
Polariton Transitions in Femtosecond Transient Absorption Studies of Ultrastrong Light–Molecule Coupling
CA DelPo, B Kudisch, KH Park, SUZ Khan, F Fassioli, D Fausti, BP Rand, GD Scholes
The Journal of Physical Chemistry Letters 11 (7), 2667-2674, 2020. Go to link ❯
Strong light–matter coupling is emerging as a fascinating way to tune optical properties and modify the photophysics of molecular systems. In this work, we studied a molecular chromophore under strong coupling with the optical mode of a Fabry–Perot cavity resonant to the first electronic absorption band. Using femtosecond pump–probe spectroscopy, we investigated the transient response of the cavity-coupled molecules upon photoexcitation resonant to the upper and lower polaritons. We identified an excited state absorption from upper and lower polaritons to a state at the energy of the second cavity mode. Quantum mechanical calculations of the many-molecule energy structure of cavity polaritons suggest assignment of this state as a two-particle polaritonic state with optically allowed transitions from the upper and lower polaritons. We provide new physical insight into the role of two-particle polaritonic states in explaining transient signatures in hybrid light–matter coupling systems consistent with analogous many-body systems.
Modifying reverse intersystem crossing with cavity polaritons.
F Fassioli Olsen, C DelPo, B Kudisch, KH Park, D Fausti, G Scholes
Bulletin of the American Physical Society, 65, 2020 Go to link ❯
Strong light-matter coupling gives rise to a superposition of light and matter states called polaritons. In the molecular setting, strong light-matter coupling is usually achieved when a large number of molecules is coupled to the same mode of an optical cavity. In this case, the energy structure is normally described as consisting of two distinct polaritonic states together with a large set of intermediate molecular dark states, that due to their purely molecular nature are believed to exhibit dynamics that resemble those of the bare molecular states. In this work we investigate the nature of these intermediate states and how their dynamics and optical response deviate from those of molecules outside the cavity. We apply our framework to simulate linear and non-linear optical responses of an experimentally studied system, namely 4CzIPN, to gain insight into how these intermediate states are involved in and modify intersystem crossing and reverse intersystem crossing under the strong light matter coupling regime.
Dynamics of phase coherence in superconducting cuprates upon mid-infrared photoexcitation.
A Montanaro, F Giusti, D Fausti
Bulletin of the American Physical Society, 65, 2020 Go to link ❯
Superconducting fluctuations in optimally-doped cuprates are known to survive well above the critical temperature, making these systems a perfect playground to investigate the possibility of transiently controlling superconductivity through ultrashort light pulses. While it has been widely shown that high photon energy electromagnetic fields melt the superconducting phase , there are evidences that mid-infrared photoexcitation can trigger the onset of superconductivity in regions of the phase diagram in which the system is not superconducting at the equilibrium [2,3]. We performed measurements on optimally-doped Y-Bi2212 by a 3-pulse technique which allows to disentangle these two effects. The approach is based on selectively destroying the superconducting state using a visible pump, and then further exciting the sample by means of a mid-infrared source. By probing the system through a broadband supercontinuum, we reveal the details of the transient dynamics of the condensate phase coherence solely driven by mid-infrared pulses with photon energy close to the superconducting gap.
 Giannetti C. et al., Advances in Physics 65, 58-238 (2016)
 Fausti D. et al., Science 331, 6014 189-191 (2011)
 Giusti F. et al., Phys. Rev. Lett. 122, 067002 (2019)
Quantum model for Impulsive Stimulated Raman Scattering
F Glerean, S Marcantoni, G Sparapassi, A Blason, M Esposito, F Benatti, D Fausti
Journal of Physics B: Atomic, Molecular and Optical Physics, 52, 14, 2019 Go to link ❯
The interaction between ultrashort light pulses and non-absorbing materials is dominated by impulsive stimulated Raman scattering (ISRS). The description of ISRS in the context of pump&probe experiments is based on effective classical models describing the interaction between the phonon and pulsed electromagnetic fields. Here we report a theoretical description of ISRS where we do not make any semi-classical approximation and we treat both photonic and phononic degrees of freedom at the quantum level. The results of the quantum model are compared with semiclassical results and validated by means of spectrally resolved pump&probe measurements on α-quartz.
Femtosecond covariance spectroscopy
J Owen Tollerud, G Sparapassi, A Montanaro, S Asban, F Glerean, F Giusti, A Marciniak, G Kourousias, F Billè, F Cilento, S Mukamel, D Fausti
Proceedings of the National Academy of Sciences 116 (12), 5383-5386, 2019 Go to link ❯
Here we establish femtosecond covariance spectroscopy as a technique that uses ultrashort stochastic light pulses to measure nonlinear material responses. By using pulses with spectrally uncorrelated fluctuations we can leverage on the noise and consider each repetition of the experiment as a measurement under different conditions. In this limit, we demonstrate that nonlinear processes in the sample can be retrieved by measuring the spectral correlations in different pulses. We validate the approach by studying stimulated Raman scattering in α-quartz. This concept can be applied to reveal low-energy modes of electronic, spin, and vibrational origin and adapted to different techniques and wavelength ranges, from optical to X-ray free-electron lasers, where strong stochastic fluctuations are unavoidable.
Localized vibrations in superconducting YB a2 Cu3 O7 revealed by ultrafast optical coherent spectroscopy
F Novelli, G Giovannetti, A Avella, F Cilento, L Patthey, M Radovic, M Capone, F Parmigiani, and D Fausti
Phys. Rev. B 95, 174524, 2017 Go to link ❯
The interaction between phonons and high-energy excitations of electronic origin in cuprates and their role in the superconducting mechanisms is still controversial. Here we use coherent vibrational time-domain spectroscopy together with density functional and dynamical mean-field theory calculations to establish a direct link between the c-axis phonon modes and the in-plane electronic charge excitations in optimally doped YBa2Cu3O7. The nonequilibrium Raman tensor is measured by means of the broadband “coherent-phonon” response in pump-probe experiments and is qualitatively described by our model using density functional theory in the frozen-phonon approximation plus single-band dynamical mean-field theory to account for the electronic correlations. The major outcome of our experimental and theoretical study is to establish the link between out-of-plane copper ion displacements and the in-plane electronic correlations, and to estimate at a few unit cells the correlation length of the associated phonon mode. The approach introduced here could help in revealing the complex interplay between fluctuations of different nature and spatial correlation in several strongly correlated materials.
Ultrafast optical spectroscopy of strongly correlated materials and high-temperature superconductors: a non-equilibrium approach
C. Giannetti, M. Capone, D. Fausti, M. Fabrizio, F. Parmigiani, D. Mihailovic
Advances in Physics 65 (2), 58-238, 2016 Go to link ❯
Here, we review the most recent achievements in the experimental and theoretical studies of the non-equilibrium electronic, optical, structural and magnetic properties of correlated materials. The focus will be mainly on the prototypical case of correlated oxides that exhibit unconventional superconductivity or other exotic phases. The discussion will extend also to other topical systems, such as iron-based and organic superconductors, MgB2 and chargetransfer insulators. Under the light of this review, the dramatically growing demand for novel experimental tools and theoretical methods, models and concepts, will clearly emerge. In particular, the necessity of extending the actual experimental capabilities and the numerical and analytic tools to microscopically treat the non-equilibrium phenomena beyond the simple phenomenological approaches represents one of the most challenging new frontier in physics.
Pulsed homodyne Gaussian quantum tomography with low detection efficiency.
M. Esposito, F. Benatti, R. Floreanini, S. Olivares, F. Randi, K. Titimbo, M. Pividori, F. Novelli, F. Cilento, F. Parmigiani, and D. Fausti
New Journal of Physics , 16, 043004, 2014 Go to link ❯
Pulsed homodyne quantum tomography usually requires a high detection efficiency, limiting its applicability in quantum optics. Here, it is shown that the presence of low detection efficiency (<50%) does not prevent the tomographic reconstruction of quantum states of light, specifically, of Gaussian states. This result is obtained by applying the so-called ‘minimax’ adaptive reconstruction of the Wigner function to pulsed homodyne detection. In particular, we prove, by both numerical and real experiments, that an effective discrimination of different Gaussian quantum states can be achieved. Our finding paves the way to a more extensive use of quantum tomographic methods, even in physical situations in which high detection efficiency is unattainable.
Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system.
F. Novelli, G. De Filippis, V. Cataudella, M. Esposito, I. Vergara,F. Cilento, E. Sindici, A. Amaricci, C. Giannetti, D. Prabhakaran, S.Wall, A. Perucchi, S. Dal Conte, G. Cerullo, M. Capone, A. Mishchenko, M. Grüninger, N. Nagaosa, F. Parmigiani, and D. Fausti
Nature Communications, 5, 5122, 2014 Go to link ❯
The non-equilibrium approach to correlated electron systems is often based on the paradigm that different degrees of freedom interact on different timescales. In this context, photo-excitation is treated as an impulsive injection of electronic energy that is transferred to other degrees of freedom only at later times. Here, by studying the ultrafast dynamics of quasi-particles in an archetypal strongly correlated charge-transfer insulator (La2CuO4+δ), we show that the interaction between electrons and bosons manifests itself directly in the photo-excitation processes of a correlated material. With the aid of a general theoretical framework (Hubbard–Holstein Hamiltonian), we reveal that sub-gap excitation pilots the formation of itinerant quasi-particles, which are suddenly dressed by an ultrafast reaction of the bosonic field.
Speed limit of the insulator–metal transition in magnetite
S. de Jong, R. Kukreja, C. Trabant, N. Pontius, C. F. Chang, T. Kachel, M. Beye, F. Sorgenfrei, C. H. Back, B. Bräuer, W. F. Schlotter, J. J. Turner, O. Krupin, M. Doehler, D. Zhu, M. A. Hossain, A. O. Scherz, D. Fausti*3, F. Novelli, M. Esposito, W. S. Lee, Y. D. Chuang, D. H. Lu, R. G. Moore, M. Yi, M. Trigo, P. Kirchmann, L. Pathey, M. S. Golden, M. Buchholz, P. Metcalf, F. Parmigiani, W. Wurth, A. Föhlisch, C. Schüßler-Langeheine & H. A. Dürr.
Nature Materials, 12, 882-886, 2013 Go to link ❯
As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator–metal, or Verwey, transition has long remained inaccessible. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase. Here we investigate the Verwey transition with pump–probe X-ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator–metal transition. We find this to be a two-step process. After an initial 300 fs destruction of individual trimerons, phase separation occurs on a 1.5±0.2 ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics.
Optical excitation of Josephson plasma solitons in a cuprate superconductor
A. Dienst, E. Casandruc, D. Fausti, L. Zhang, M. Eckstein, M. Hoffmann, V. Khanna, N. Dean, M. Gensch, S. Winnerl, W. Seidel, S. Pyon, T. Takayama, H. Takagi & A. Cavalleri.
Nature Materials, 12, 535-541 (2013) Go to link ❯
Josephson plasma waves are linear electromagnetic modes that propagate along the planes of cuprate superconductors, sustained by interlayer tunnelling supercurrents. For strong electromagnetic fields, as the supercurrents approach the critical value, the electrodynamics become highly nonlinear. Josephson plasma solitons (JPSs) are breather excitations predicted in this regime, bound vortex–antivortex pairs that propagate coherently without dispersion. We experimentally demonstrate the excitation of a JPS in La1.84Sr0.16CuO4, using intense narrowband radiation from an infrared free-electron laser tuned to the 2-THz Josephson plasma resonance. The JPS becomes observable as it causes a transparency window in the opaque spectral region immediately below the plasma resonance. Optical control of magnetic-flux-carrying solitons may lead to new applications in terahertz-frequency plasmonics, in information storage and transport and in the manipulation of high-Tcsuperconductivity.
Two-colour pump–probe experiments with a twin-pulse-seed extreme ultraviolet free-electron laser
E Allaria, F Bencivenga, R Borghes, F Capotondi, D Castronovo, P Charalambous, P Cinquegrana, MB Danailov, G De Ninno, A Demidovich, S Di Mitri, B Diviacco, D Fausti, WM Fawley, E Ferrari, L Froehlich, D Gauthier, A Gessini, L Giannessi, R Ivanov, N Kiskinova, G Kurdi, B Mahieu, N Mahne, I Nikolov, C Masciovecchio, E Pedersoli, G Penco, L Raimondi, C Serpico, P Sigalotti, S Spampinati, C Spezzani, C Svetina, M Trovò, M Zangrando
Nature communications 4, 2476, 2013 Go to link ❯
Exploring the dynamics of matter driven to extreme non-equilibrium states by an intense ultrashort X-ray pulse is becoming reality, thanks to the advent of free-electron laser technology that allows development of different schemes for probing the response at variable time delay with a second pulse. Here we report the generation of two-colour extreme ultraviolet pulses of controlled wavelengths, intensity and timing by seeding of high-gain harmonic generation free-electron laser with multiple independent laser pulses. The potential of this new scheme is demonstrated by the time evolution of a titanium-grating diffraction pattern, tuning the two coherent pulses to the titanium M-resonance and varying their intensities. This reveals that an intense pulse induces abrupt pattern changes on a time scale shorter than hydrodynamic expansion and ablation. This result exemplifies the essential capabilities of the jitter-free multiple-colour free-electron laser pulse sequences to study evolving states of matter with element sensitivity.
Light-Induced Superconductivity in a Stripe-Ordered Cuprate.
D. Fausti, R. I. Tobey, N. Dean, S. Kaiser, A. Dienst, M. Hoffmann, S. Pyon, T. Takayama, H. Takagi, A. Cavalleri
Science 331, 189, 2011 Go to link ❯
One of the most intriguing features of some high-temperature cuprate superconductors is the interplay between one-dimensional “striped” spin order and charge order, and superconductivity. We used mid-infrared femtosecond pulses to transform one such stripe-ordered compound, nonsuperconducting La1.675Eu0.2Sr0.125CuO4, into a transient three-dimensional superconductor. The emergence of coherent interlayer transport was evidenced by the prompt appearance of a Josephson plasma resonance in the c-axis optical properties. An upper limit for the time scale needed to form the superconducting phase is estimated to be 1 to 2 picoseconds, which is significantly faster than expected. This places stringent new constraints on our understanding of stripe order and its relation to superconductivity.