The SPS Award committee chaired by Professor Minh Quang Tran selected the winners for 2019 out of many submissions.
The winners presented their work at the Joint Annual Meeting in Zürich. Below are the summaries written by the winners.
The SPS Award in General Physics is given to Matteo Fadel for his work on "Quantum metrology and non-classical correlations in ultracold atomic ensembles".
Quantum correlations in many-body systems: theory and experiments
Quantum correlations can be so strong that they go beyond our classical intuition. In fact, these correlations are not observed in our everyday lives in the macroscopic world: why? This question motivates the investigation of quantum correlations in many-body systems, which are interesting for both fundamental research and practical applications: they allow to investigate the validity range of quantum mechanics and they are a resource for tasks that are inaccessible by classical means.
Three different types of nonclassical correlations have been identified, namely entanglement, Einstein-Podolsky-Rosen (EPR) correlations, and Bell correlations. Preparing and observing such correlations in many-body systems is challenging. Some of the difficulties lie in the complexity of manipulating fragile many-body quantum systems, and in the need to conclude correlations between the individually inaccessible constituents from collective properties of the system.
My doctoral thesis was devoted to the experimental and theoretical investigation of quantum correlations in many-body systems. Together with my colleagues, I reported experiments where we prepare Bose-Einstein condensates (BECs) of approximately 600 Rubidium-87 atoms in a spin-squeezed state, and analyse the correlations between the constituent atoms. The results obtained during my doctorate show how entanglement, EPR-steering and Bell correlations can be detected and characterised in many-body systems, and open new possibilities for the characterisation of multipartite quantum states. As a first major result, we derived practical witnesses for Bell correlations, involving collective measurements on the entire system, which we then tested experimentally in our BECs . We show the experimental detection of Bell correlations in a BEC of approximately 500 atoms, therefore demonstrating that such correlations can be prepared and detected in many-body systems.
The concept of correlations in ensembles of indistinguishable particles, as in the case of BECs, has been discussed controversially, and its usefulness for quantum technologies other than metrology has been questioned. Therefore, as a second major result, we showed experimentally how correlations in a system of indistinguishable particles can be extracted into spatially separated (and therefore distinguishable) regions, and used to demonstrate EPR steering between two ensembles of approximately 300 atoms each . Apart from being the first observation of steering between two mesoscopic systems, our result shows that the splitting of atomic ensembles in nonclassical states can be used to share quantum correlations enabling tasks such as quantum teleportation and one-side device-independent communication.
 R. Schmied, J.-D. Bancal, B. Allard, M. Fadel, V. Scarani, P. Treutlein and N. Sangouard, Science 352, 441 (2016)
 M. Fadel, T. Zibold, B. Décamps and P. Treutlein, Science 360, 409 (2018)
Edoardo Baldini received the SPS Award in Condensed Matter Physics for his work on "Nonequilibrium Dynamics of Collective Excitations in Strongly Interacting and Correlated Quantum Systems".
Nonequilibrium Dynamics of Collective Excitations in Quantum Materials
Unveiling the origin of exotic phenomena in quantum materials is a subject of tremendous interest for the design and control of advanced functionalities in future devices. However, the presence of strong interactions among charge, spin, orbital and lattice degrees of freedom renders quantum materials a puzzling case to understand. The most promising strategy to address the complexity of this many-body problem is revealing how the electrons in this class of solids interact among themselves and with other elementary excitations. In this respect, spectroscopy under equilibrium conditions has dominated the research in the field for decades, monitoring the energy-momentum dispersion of fundamental elementary excitations. Nevertheless, this equilibrium approach suffers from several intrinsic limitations, as it provides only a time-averaged picture of the underlying dynamics and hinders the possibility to disentangle the contributions of spectrally-overlapping excitations. Key to overcome these limitations is the design of a tailored nonequilibrium approach that can address the fundamental paradigm of quantum materials. Potentially, one needs a technique that can separate the spectroscopic fingerprints of different degrees of freedom while simultaneously mapping the low- and high-energy scales with ultrafast temporal resolution, an approach that has been lacking so far. To address this problem, here we present a novel laser-based nonequilibrium method in which the ultrafast changes in the optical spectrum of a quantum material are mapped with a time resolution of <50 fs over an ultrabroad range. This allows for unraveling mutual couplings between distinct low- and high-energy collective modes and achieving new manipulation schemes of fundamental excitations in technology. Special emphasis will be given to the rising fields of excitonics and phononics in materials governed by strong interactions and correlations .
 E. Baldini, Nonequilibrium Dynamics of Collective Excitations in Quantum Materials (Springer, 2018)
The SPS Award in Applied Physics is given to Shadi Fatayer for his work on "High precision experiments with zeptoampere resolution using Atomic Force Microscopy".
Investigating charge-state transitions of molecules on insulating films by atomic force microscopy
The electronic properties of adsorbates on surfaces are crucial for applications in molecular electronics, photo-conversion and catalysis. Molecular devices benefit from molecules on top of non-conductive substrates, to avoid charge leakage. Experimentally, the electronic properties of adsorbates can be studied by, for example, photoemission and scanning tunneling microscopy. Yet these techniques do not allow for measurements on insulators.
Based on the atomic force microscope (AFM), we developed a method to investigate the electronic properties of individual adsorbates on insulators. We demonstrated that molecular charge states, including doubly charged states, can be both controlled and determined with the AFM. Importantly, to gather quantitative information, we developed a method to perform tunneling spectroscopy with the AFM. The AFM is employed as an ultra-low current meter based on counting single-electron tunneling events in real time . The analogous currents measured are in the zeptoampere range.
In this way, we could quantify the reorganization energy of a single molecule on an insulator . The reorganization energy is a crucial parameter in determining electron-transfer rates. Besides quantifying the electronic properties of single adsorbates on insulating films, our work provides insight into single-electron transfer processes and suggests ways to tune and manipulate energy transfer rates between molecules.
Moreover, we employed charge-state control to perform unconventional on-surface chemical reactions of molecules on insulators . By attaching and detaching electrons from the AFM tip to the molecule we demonstrated control over bond cleavage and formation.
 S. Fatayer et al. Nature Nanotechnology 13, 376-380 (2018)
 S. Fatayer et al. Physical Review Letters 121, 226101 (2018)
Ileana-Cristina Benea-Chelmus is honored with the SPS Award related to Metrology for her work on "Terahertz quantum optics with ultrashort pulses".
Terahertz quantum optics in the time-domain
One of the most fundamental yet peculiar concepts in quantum mechanics is the existence of vacuum field fluctuations. Owing to Heisenberg uncertainty, a fluctuating electromagnetic field is characteristic to the ground state of light even in a vacuum. The ground state contains zero photons and an intensity measurement thereof yields zero. The existence of vacuum field fluctuations was confirmed through indirect phenomena such as the Casimir force or the Lamb shift. To detect them directly, ultrafast field detectors are required.
In this work we measure, for the first time, the amplitude on these fluctuations at terahertz frequencies, and then investigate how these fluctuations are correlated across time and space . This measurement gives access to their spectrum and spatial coherence - quantities that influence effects related to vacuum fields. The technique exploits the electro-optic effect introduced by the vacuum electric field in a crystal.
We demonstrate that a non-zero field coherence is reminiscent even after all classical light has been removed from the system - a clear signature of ground state properties in the quantum picture. Our results agree quantitatively with the quantum theory. This endeavor implied extreme experimental measures: the detection crystal was placed inside a closed-cycle Helium-3 cryostat to shield and suppress any classical radiation. Moreover, all elements were maximally optimised to work at the absolute quantum noise limit for measurement times > 10000 s. The field sensitivity is record-high (0.25 V/m). The technique gives unparalleled information about the coherence of vacuum fields but was first benchmarked for classical fields. The initial demonstration allowed the observation of a transition from Poissonian photon statistics to bunching in a laser system . In parallel, we develop ultra-sensitive field detectors that make use of nanofabrication to open up the field to cavity electrodynamics experiments in the time-domain.
 I.-C. Benea-Chelmus et al., Electric field correlation measurements on the electromagnetic vacuum state, Nature 568, 202-206 (2019)
 I.-C. Benea-Chelmus et al., Subcycle measurement of intensity correlations in the terahertz frequency range, Phys. Rev. A 93, 043812 (2016)
The SPS Award in Computational Physics is given to Amir H. Ghadimi for his work on " Elastic strain engineering for ultra-low mechanical dissipation".
Ultra-coherent micro-mechanical resonators for quantum information processing at room temperature
Elastic strain engineering utilizes stress to realize unusual material properties. For instance, strain can be used to enhance the electron mobility of a semiconductor thin film, enabling more efficient solar cells and smaller, faster transistors. In the context of nanomechanics, the pursuit of resonators with ultra-high coherence has led to intense study of a complementary strain engineering technique, “dissipation dilution”, whereby the stiffness of a material is effectively increased without added loss. Dissipation dilution is known to underly the anomalously high quality factor of nanomechanical resonators including recently-developed “soft-clamped” resonators ; however, the paradigm has to date relied on weak strain naturally produced during material synthesis. By contrast, the use of geometric strain engineering techniques—capable of producing local stresses near the material yield strength—remains largely unexplored.
In this work, we show that geometric strain engineering combined with soft-clamping can produce unprecedentedly high quality factor nanomechanical resonators . Specifically, using a spatially non-uniform phononic crystal pattern, we co-localize the strain and flexural motion of a SiN nanobeam, while increasing the former to near the yield strength. This combined approach produces string-like resonators with room-temperature Q × f products above1015 Hz, far exceeding previous values for a mechanical oscillator of any size and any type. The devices we have realized can have room temperature force sensitivities of ~1 aN / √Hz, perform hundreds of quantum coherent cycles at room temperature, and attain Q ~ 109 (1 billion) at megahertz frequencies. These results signal a paradigm shift in the ability to control dissipation in nanomechanical systems, with applications ranging from quantum information processing, precision force microscopy to tests of quantum gravity. Combining the reported approach with crystalline or 2D materials may lead to further, possibly substantial, improvements.
 Y. Tsaturyan, A. Barg, E. S. Polzik, and A. Schliesser, "Ultracoherent nanomechanical resonators via soft clamping and dissipation dilution," Nature Nanotechnology, vol. 12, no. 8, pp. 776–783, Jun. 2017.
 A. H. Ghadimi et al., "Elastic strain engineering for ultralow mechanical dissipation," Science, vol. 360, no. 6390, pp. 764–768, May 2018.