Publications


Double-sided coaxial circuit QED with out-of-plane wiring

APPLIED PHYSICS LETTERS 110 (2017) ARTN 222602

J Rahamim, T Behrle, MJ Peterer, A Patterson, PA Spring, T Tsunoda, R Manenti, G Tancredi, PJ Leek


Generation and detection of squeezed phonons in lattice dynamics by ultrafast optical excitations

New Journal of Physics 19 (2017)

F Benatti, M Esposito, D Fausti, R Floreanini, K Titimbo, K Zimmermann

© 2017 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. We propose a fully quantum treatment for pump and probe experiments applied to the study of phonon excitations in solids. To describe the interaction between photons and phonons, a single effective hamiltonian is used that is able to model both the excitation induced by pump laser pulses and the subsequent measuring process through probe pulses. As the photoexcited phonons interact with their surroundings, mainly electrons and impurities in the target material, they cannot be considered isolated: their dynamics needs to be described by a master equation that takes into account the dissipative and noisy effects due to the presence of the environment. In this formalism, the quantum dynamics of pump excited phonons can be analyzed through suitable probe photon observables; in particular, a clear signature of squeezed phonons can be obtained by looking simultaneously at the behavior of the scattered probe mean photon number and its variance.


Probing the Fluctuations of Optical Properties in Time-Resolved Spectroscopy

Physical Review Letters 119 (2017)

F Randi, M Esposito, F Giusti, O Misochko, F Parmigiani, D Fausti, M Eckstein

© 2017 American Physical Society. We show that, in optical pump-probe experiments on bulk samples, the statistical distribution of the intensity of ultrashort light pulses after interaction with a nonequilibrium complex material can be used to measure the time-dependent noise of the current in the system. We illustrate the general arguments for a photoexcited Peierls material. The transient noise spectroscopy allows us to measure to what extent electronic degrees of freedom dynamically obey the fluctuation-dissipation theorem, and how well they thermalize during the coherent lattice vibrations. The proposed statistical measurement developed here provides a new general framework to retrieve dynamical information on the excited distributions in nonequilibrium experiments, which could be extended to other degrees of freedom of magnetic or vibrational origin.


Optimal control of two qubits via a single cavity drive in circuit quantum electrodynamics

PHYSICAL REVIEW A 95 (2017) ARTN 042325

JL Allen, R Kosut, J Joo, P Leek, E Ginossar


Circuit quantum acoustodynamics with surface acoustic waves.

Nature communications 8 (2017) 975-

R Manenti, AF Kockum, A Patterson, T Behrle, J Rahamim, G Tancredi, F Nori, PJ Leek

The experimental investigation of quantum devices incorporating mechanical resonators has opened up new frontiers in the study of quantum mechanics at a macroscopic level. It has recently been shown that surface acoustic waves (SAWs) can be piezoelectrically coupled to superconducting qubits, and confined in high-quality Fabry-Perot cavities in the quantum regime. Here we present measurements of a device in which a superconducting qubit is coupled to a SAW cavity, realising a surface acoustic version of cavity quantum electrodynamics. We use measurements of the AC Stark shift between the two systems to determine the coupling strength, which is in agreement with a theoretical model. This quantum acoustodynamics architecture may be used to develop new quantum acoustic devices in which quantum information is stored in trapped on-chip acoustic wavepackets, and manipulated in ways that are impossible with purely electromagnetic signals, due to the 105 times slower mechanical waves.In this work, Manenti et al. present measurements of a device in which a tuneable transmon qubit is piezoelectrically coupled to a surface acoustic wave cavity, realising circuit quantum acoustodynamic architecture. This may be used to develop new quantum acoustic devices.


Strong Coupling of Microwave Photons to Antiferromagnetic Fluctuations in an Organic Magnet.

Physical review letters 119 (2017) 147701-

M Mergenthaler, J Liu, JJ Le Roy, N Ares, AL Thompson, L Bogani, F Luis, SJ Blundell, T Lancaster, A Ardavan, GAD Briggs, PJ Leek, EA Laird

Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4 K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions. These results show that multispin modes in organic crystals are suitable for circuit QED, offering a platform for their coherent manipulation. They also utilize the circuit QED architecture as a way to probe spin correlations at low temperature.


Simultaneous Bistability of a Qubit and Resonator in Circuit Quantum Electrodynamics

Physical Review Letters 118 (2017)

TK Mavrogordatos, G Tancredi, M Elliott, MJ Peterer, A Patterson, J Rahamim, PJ Leek, E Ginossar, MH Szymańska


Phase separation in the nonequilibrium Verwey transition in magnetite

Physical Review B 93 (2016)

F Randi, I Vergara, F Novelli, M Esposito, M Dell'Angela, VAM Brabers, P Metcalf, R Kukreja, HA Dürr, D Fausti, M Grüninger, F Parmigiani

© 2016 American Physical Society. We present equilibrium and out-of-equilibrium studies of the Verwey transition in magnetite. In the equilibrium optical conductivity, we find a steplike change at the phase transition for photon energies below about 2 eV. The possibility of triggering a nonequilibrium transient metallic state in insulating magnetite by photo excitation was recently demonstrated by an x-ray study. Here we report a full characterization of the optical properties in the visible frequency range across the nonequilibrium phase transition. Our analysis of the spectral features is based on a detailed description of the equilibrium properties. The out-of-equilibrium optical data bear the initial electronic response associated to localized photoexcitation, the occurrence of phase separation, and the transition to a transient metallic phase for excitation density larger than a critical value. This allows us to identify the electronic nature of the transient state, to unveil the phase transition dynamics, and to study the consequences of phase separation on the reflectivity, suggesting a spectroscopic feature that may be generally linked to out-of-equilibrium phase separation.


Surface acoustic wave resonators in the quantum regime

PHYSICAL REVIEW B 93 (2016) ARTN 041411(R)

R Manenti, MJ Peterer, A Nersisyan, EB Magnusson, A Patterson, PJ Leek


Erratum: Photon number statistics uncover the fluctuations in non-equilibrium lattice dynamics (Nature Communications (2015) 6:10249 DOI: 10.1038/ncomms10249)

Nature Communications 7 (2016)

M Esposito, K Titimbo, K Zimmermann, F Giusti, F Randi, D Boschetto, F Parmigiani, R Floreanini, F Benatti, D Fausti


Quantum interferences reconstruction with low homodyne detection efficiency

EPJ Quantum Technology 3 (2016)

M Esposito, F Randi, K Titimbo, G Kourousias, A Curri, R Floreanini, F Parmigiani, D Fausti, K Zimmermann, F Benatti


Photon number statistics uncover the fluctuations in non-equilibrium lattice dynamics.

Nature communications 6 (2015) 10249-

M Esposito, K Titimbo, K Zimmermann, F Giusti, F Randi, D Boschetto, F Parmigiani, R Floreanini, F Benatti, D Fausti

Fluctuations of the atomic positions are at the core of a large class of unusual material properties ranging from quantum para-electricity to high temperature superconductivity. Their measurement in solids is the subject of an intense scientific debate focused on seeking a methodology capable of establishing a direct link between the variance of the atomic displacements and experimentally measurable observables. Here we address this issue by means of non-equilibrium optical experiments performed in shot-noise-limited regime. The variance of the time-dependent atomic positions and momenta is directly mapped into the quantum fluctuations of the photon number of the scattered probing light. A fully quantum description of the non-linear interaction between photonic and phononic fields is benchmarked by unveiling the squeezing of thermal phonons in α-quartz.


Quantum optics for studying ultrafast processes in condensed matter

Conference on Lasers and Electro-Optics Europe - Technical Digest 2015-August (2015)

M Esposito, F Randi, F Giusti, D Boschetto, F Parmigiani, D Fausti

© 2015 OSA. Quantum state reconstruction techniques are used to address non equilibrium matter states. Proof of principle experiments reveal that few photons coherent pulses can be squeezed by the interaction with impulsively excited coherent phonons in quartz.


Quantum optics for studying ultrafast processes in condensed matter

CLEO: QELS - Fundamental Science, CLEO_QELS 2015 (2015) 1551p-

M Esposito, F Randi, F Giusti, D Boschetto, F Parmigiani, D Fausti

Quantum state reconstruction techniques are used to address non equilibrium matter states. Proof of principle experiments reveal that few photons coherent pulses can be squeezed by the interaction with impulsively excited coherent phonons in quartz. © 2014 Optical Society of America.


Surface acoustic wave devices on bulk ZnO crystals at low temperature

APPLIED PHYSICS LETTERS 106 (2015) ARTN 063509

EB Magnusson, BH Williams, R Manenti, M-S Nam, A Nersisyan, MJ Peterer, A Ardavan, PJ Leek


Coherence and decay of higher energy levels of a superconducting transmon qubit.

Physical review letters 114 (2015) 010501-

MJ Peterer, SJ Bader, X Jin, F Yan, A Kamal, TJ Gudmundsen, PJ Leek, TP Orlando, WD Oliver, S Gustavsson

We present measurements of coherence and successive decay dynamics of higher energy levels of a superconducting transmon qubit. By applying consecutive π pulses for each sequential transition frequency, we excite the qubit from the ground state up to its fourth excited level and characterize the decay and coherence of each state. We find the decay to proceed mainly sequentially, with relaxation times in excess of 20  μs for all transitions. We also provide a direct measurement of the charge dispersion of these levels by analyzing beating patterns in Ramsey fringes. The results demonstrate the feasibility of using higher levels in transmon qubits for encoding quantum information.


Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system.

Nature communications 5 (2014) 5112-

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, D Fausti

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 (La2CuO(4+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.


Pulsed homodyne Gaussian quantum tomography with low detection efficiency

New Journal of Physics 16 (2014)

M Esposito, F Benatti, R Floreanini, S Olivares, F Randi, K Titimbo, M Pividori, F Novelli, F Cilento, F Parmigiani, D Fausti

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. © 2014 IOP Publishing Ltd.


Speed limit of the insulator-metal transition in magnetite.

Nature materials 12 (2013) 882-886

S de Jong, R Kukreja, C Trabant, N Pontius, CF Chang, T Kachel, M Beye, F Sorgenfrei, CH Back, B Bräuer, WF Schlotter, JJ Turner, O Krupin, M Doehler, D Zhu, MA Hossain, AO Scherz, D Fausti, F Novelli, M Esposito, WS Lee, YD Chuang, DH Lu, RG Moore, M Yi, M Trigo, P Kirchmann, L Pathey, MS Golden, M Buchholz, P Metcalf, F Parmigiani, W Wurth, A Föhlisch, C Schüßler-Langeheine, HA Dürr

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.


Applied physics. Storing quantum information in Schrödinger's cats.

Science 342 (2013) 568-569

PJ Leek

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