A5057680476- Quantum Information and Cryptography
- Quantum Mechanics and Applications
- Quantum Computing Algorithms and Architecture
- Mechanical and Optical Resonators
- Quantum optics and atomic interactions
- Advanced Thermodynamics and Statistical Mechanics
- Quantum and electron transport phenomena
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum-Dot Cellular Automata
- Neural dynamics and brain function
- Photonic and Optical Devices
- Advanced Fluorescence Microscopy Techniques
- Computability, Logic, AI Algorithms
- Neural Networks and Reservoir Computing
- Quantum many-body systems
- Fault Detection and Control Systems
- Electronic and Structural Properties of Oxides
- Philosophy and History of Science
- Statistical Methods in Clinical Trials
- Semiconductor materials and devices
- Strong Light-Matter Interactions
- Random lasers and scattering media
- Advanced Optical Sensing Technologies
- Semiconductor Quantum Structures and Devices
- Spectroscopy and Quantum Chemical Studies
University of Geneva
2011-2025
Terra Quantum (Switzerland)
2023
University of Basel
2018-2022
Universität Innsbruck
2014-2018
Large-scale quantum effects have always played an important role in the foundations of theory. With recent experimental progress and aspiration for enhanced applications, interest macroscopic has been reinforced. In this review, measures aiming to quantify various aspects quantumness are critically analyzed discussed. Recent results on difficulties prospects create, maintain, detect states surveyed. The foundational questions as well practical applications is outlined. Finally, past ongoing...
We report on an elementary quantum network of two atomic ions separated by 230 m. The are trapped in different buildings and connected with 520(2) m optical fiber. At each node, the electronic state ion is entangled polarization a single cavity photon; subsequent to interference photons at beam splitter, photon detection heralds entanglement between ions. Fidelities up (88.0+2.2-4.7)% achieved respect maximally Bell state, success probability 4×10^{-5}. analyze routes improve these metrics,...
Quantum metrology is a technique for using principles of quantum theory to make ultraprecise measurements physical systems, however, its effectiveness frequently hampered by environmental noise. A new theoretical analysis provides criteria knowing whether noise will impact measurement and if corrections are possible.
We propose an experimentally accessible scheme to determine the lower bounds on quantum Fisher information (QFI), which ascertains multipartite entanglement or usefulness for metrology. The is based comparing measurement statistics of a state before and after small unitary rotation. argue that, in general, limited resolution collective observables prevents detection large QFI. This can be overcome by performing additional operation prior measurement. illustrate power this protocol...
We establish general limits on how precise a parameter, e.g. frequency or the strength of magnetic field, can be estimated with aid full and fast quantum control. consider uncorrelated noisy evolutions N qubits show that control allows to fully restore Heisenberg scaling (~1/N^2) for all rank-one Pauli noise except dephasing. For other types asymptotic enhancement is unavoidably limited constant-factor improvement over standard limit (~1/N) even when allowing power The latter holds both in...
Using quantum systems as sensors or probes has been shown to greatly improve the precision of parameter estimation by exploiting unique features such entanglement. A major task in sensing is design optimal protocol, i.e., most precise one. It solved for some specific instances problem, but general even numerical methods are not known. Here, we focus on single-shot Bayesian setting, where goal find initial state probe (which can be entangled with an auxiliary system), measurement, and...
Displaced single-photon entanglement is a simple form of optical entanglement, obtained by sending photon on beamsplitter and subsequently applying displacement operation. We show that it can generate, through momentum transfer in the pulsed regime, an optomechanical entangled state involving macroscopically distinct mechanical components, even if system operates weak coupling regime. discuss experimental feasibility this approach might open up way for testing unconventional decoherence models.
Quantum metrology offers a quadratic advantage over classical approaches to parameter estimation problems by utilising entanglement and nonclassicality. However, the hurdle of actually implementing necessary quantum probe states measurements, which vary drastically for different metrological scenarios, is usually not taken into account. We show that wide range tasks in metrology, 2D cluster (a particular family useful measurement-based computation) can serve as flexible resources allow one...
Bell's theorem has been proposed to certify, in a device-independent and robust way, blocks either producing or measuring quantum states. In this Letter, we provide method based on certify coherent operations for the storage, processing, transfer of information. This completes set tools needed all building computer. Our distinguishes itself by its robustness experimental imperfections, so could be used that today's devices are qualified usage future computers.
Device-independent quantum key distribution aims at providing security guarantees even when using largely uncharacterised devices. In the simplest scenario, these are derived from CHSH score, which is a simple linear combination of four correlation functions. We here derive proof generalisation effectively takes into account individual values two show that this additional information, anyway available in practice, allows one to get higher rates than with score. discuss potential advantage...
We show theoretically that a large Bell inequality violation can be obtained with human eyes as detectors, in ``micro-macro'' experiment where one photon from an entangled pair is greatly amplified via stimulated emission. The robust under loss. This leads to apparent paradox, which we resolve by noting the proves existence of entanglement before amplification. same true for micro-macro experiments performed so far conventional detectors. However, also prove there genuine even high
Observing quantum effects such as superpositions and entanglement in macroscopic systems requires not only a system that is well protected against environmental decoherence, but also sufficient measurement precision. Motivated by recent experiments, we study the of coarse-graining photon number measurements on observability micro-macro created greatly amplifying one from an entangled pair. We compare results obtained for unitary cloner, which generates entanglement, measure-and-prepare...
Entanglement between macroscopically populated states can easily be created by combining a single photon and bright coherent state on beamsplitter. Motivated the simplicity of this technique, we report method using displacement operations in phase space basic detections to reveal such an entanglement. We show that eminently feasible approach provides attractive way for exploring entanglement at various scales, ranging from 1 1000 photons. This offers instructive viewpoint gain insight into...
Single-photon entangled states, i.e., states describing two optical paths sharing a single photon, constitute the simplest form of entanglement. Yet they provide valuable resource in quantum information science. Specifically, lie at heart networks, as can be used for teleportation, swapped, and purified with linear optics. The main drawback such entanglement is difficulty measuring it. Here, we present experimentally test an witness allowing one to say whether given state path also that lies...
We consider the usage of dynamical decoupling in quantum metrology, where joint evolution system plus environment is described by a Hamiltonian. show that ultra-fast unitary control operations acting locally only on qubits, noise can be eliminated while desired reduced at most constant factor, leading to Heisenberg scaling. identify all kinds such an approach applicable. Only generated Hamiltonian estimated itself cannot altered. However, even for parallel noise, one achieve improved scaling...
Device-independent quantum key distribution provides security even when the equipment used to communicate over channel is largely uncharacterized. An experimental demonstration of device-independent however challenging. A central obstacle in photonic implementations that global detection efficiency, i.e., probability signals sent are successfully received, must be above a certain threshold. We here propose method significantly relax this threshold, while maintaining provable security. This...
This paper shows that signals with a specific spatial dependence can be directly measured quadratic quantum advantage by preparing appropriate states utilize entanglement between sensors, hence the measurement process is not affected other signals, including noise, different dependence.
The efficient generation of high-fidelity entangled states is the key element for long-distance quantum communication, computation, and other technologies, at same time most resource-consuming part in many schemes. We present a class entanglement-assisted entanglement purification protocols that can generate from noisy, finite-size ensembles with improved yield fidelity as compared to previous approaches. scheme utilizes high-dimensional auxiliary perform entangling nonlocal measurements...
The security of finite-length keys is essential for the implementation device-independent quantum key distribution (DIQKD). Presently, there are several finite-size DIQKD proofs, but they mostly focused on standard protocols and do not directly apply to recent improved based noisy preprocessing, random measurements, modified CHSH inequalities. Here, we provide a general proof that can simultaneously encompass these approaches, using tighter bounds than previous analyses. In doing so, develop...
Quantum nonlocality can be demonstrated without inputs (i.e., each party using a fixed measurement setting) in network with independent sources. Here we consider this effect on ring networks, and show that the underlying quantum strategy partially characterized, or self-tested, from observed correlations. Applying these results to triangle allows us nonlocal distribution of Renou et al. [Phys. Rev. Lett. 123, 140401 (2019)PRLTAO0031-900710.1103/PhysRevLett.123.140401] requires (i) all...
Bell inequalities play a key role in certifying quantum properties for device-independent information protocols. It is still major challenge, however, to devise tailored an arbitrary given state. Existing approaches based on sums of squares provide results this direction, but they are restricted by the necessity first choosing measurement settings suited Here, we show how sum square property can be enforced target state making appropriate choice nullifiers, which made possible leaving...