Papers by stefano osnaghi
Resumo: Os principais aspectos do "problema da medição" na mecânica quântica são analisados em um... more Resumo: Os principais aspectos do "problema da medição" na mecânica quântica são analisados em uma perspectiva inspirada na filosofia transcendental e no pragmatismo lingüístico de viés wittgensteiniano, na trilha dos trabalhos de M. Bitbol. O objetivo é mostrar que a própria formulação do problema pressupõe um esquema epistemológico pré-critico -ou seja -um esquema que associa a objetividade do conhecimento cientifico à sua capacidade de descrever adequadamente uma realidade pré-estruturada. Típica desse esquema é uma concepção representacionalista das teorias, compartilhada pelas abordagens realistas e instrumentalistas tradicionais. A explicitação das raízes pragmáticas e operacionais da objetividade -raízes que são intrinsecamente ligadas às finalidades preditivas da física e que exercem sobre ela fortes vínculos constitutivos -além de facilitar a dissolução dos aspectos paradoxais do problema da medição, abre a via a uma reflexão mais geral sobre a racionalidade da física, a estrutura matemática das teorias e sua dinâmica histórica. Palavras-chave: Física quântica. Problema da medição. Objetividade. Filosofia transcendental. Pragmatismo. Representacionalismo.
Studies in History and Philosophy of Modern Physics, 2009
In 1956, Hugh Everett, then a PhD student at Princeton, proposed his ''relative state'' formulati... more In 1956, Hugh Everett, then a PhD student at Princeton, proposed his ''relative state'' formulation of quantum mechanics. John Wheeler, who was Everett's advisor, recognized the originality and importance of such a proposal, but he denied that its non-conventional approach to measurement questioned the orthodox view. Indeed, Wheeler made serious efforts to obtain the blessing of Niels Bohr for Everett's ideas. These efforts gave rise to a lively debate with the Copenhagen group, the existence and content of which have been only recently disclosed by the discovery of unpublished documents. The analysis of such documents opens a window on the conceptual background of Everett's proposal, and illuminates at the same time some crucial aspects of the Copenhagen view of the measurement problem. Also, it provides an original insight into the interplay between philosophical and social factors which underlay the postwar controversies on the interpretation of quantum mechanics.
Applied Physics Letters, 2007
We have built a microwave Fabry-Perot resonator made of diamond-machined copper mirrors coated wi... more We have built a microwave Fabry-Perot resonator made of diamond-machined copper mirrors coated with superconducting niobium. Its damping time (Tc = 130 ms at 51 GHz and 0.8 K) corresponds to a finesse of 4.6 × 10 9 , the highest ever reached for a Fabry-Perot in any frequency range. This result opens many perspectives for quantum information processing, decoherence and non-locality studies.
Physical Review Letters, 2002
We have measured the complete Wigner function W of the vacuum and of a single-photon state for a ... more We have measured the complete Wigner function W of the vacuum and of a single-photon state for a field stored in a high-Q cavity. This experiment implements the direct Lutterbach and Davidovich method [L. G. Lutterbach and L. Davidovich, Phys. Rev. Lett. 78, 2547] and is based on the dispersive interaction of a single circular Rydberg atom with the cavity field. The nonclassical nature of the single-photon field is exhibited by a region of negative W values. Extensions to other nonclassical cavity field states are discussed.
We have built a microwave Fabry-Perot resonator made of diamond-machined copper mirrors coated wi... more We have built a microwave Fabry-Perot resonator made of diamond-machined copper mirrors coated with superconducting niobium. Its damping time (Tc = 130 ms at 51 GHz and 0.8 K) corresponds to a finesse of 4.6 e9, the highest ever reached for a Fabry-Perot in any frequency range. We have tested this resonator by sending across it two circular Rydberg atoms, the first emitting a photon and the second absorbing it after a delay of 1/10 s. This long storage time photon box opens novel perspectives for quantum information. It can be used to perform sequences of hundreds of gate operations on individual atomic qubits. A set-up with one or two photon boxes can store mesoscopic fields made of hundreds of photons for decoherence and non-locality studies.
Physical Review Letters, 2002
A two-photon Fock state is prepared in a cavity sustaining a "source mode" and a "target mode," w... more A two-photon Fock state is prepared in a cavity sustaining a "source mode" and a "target mode," with a single circular Rydberg atom. In a third-order Raman process, the atom emits a photon in the target while scattering one photon from the source into the target. The final two-photon state is probed by measuring by Ramsey interferometry the cavity light shifts induced by the target field on the same atom. Extensions to other multiphoton processes and to a new type of micromaser are briefly discussed.
We present the experimental realisation of a cavity QED atom interferometer based on two consecut... more We present the experimental realisation of a cavity QED atom interferometer based on two consecutive resonant interactions of a circular Rydberg atom with the field mode of a high Q microwave resonator that is initially prepared in the vacuum state. The interferometer scheme is analogous to the Ramsey method with the classical field replaced by the quantum field stored in the cavity mode. We demonstrate the possibility to use this technique to probe, by dispersive interaction, the field stored in a second mode of the resonator.
Physical Review A, 2000
Following a proposal by two of us [L. G. Lutterbach and L. Davidovich, Phys. Rev. Lett. 78, 2547 ... more Following a proposal by two of us [L. G. Lutterbach and L. Davidovich, Phys. Rev. Lett. 78, 2547 (1997)], we have measured the Wigner function at the origin of phase space for a single photon field. Its value is negative, exhibiting the nonclassical nature of this state. The experiment is based on the absorption-free detection of the microwave field stored
Physical Review Letters, 1999
We have realized a quantum phase gate operating on quantum bits carried by a single Rydberg atom ... more We have realized a quantum phase gate operating on quantum bits carried by a single Rydberg atom and a zero-or one-photon field in a high-Q cavity. The gate operation is based on the dephasing of the atom-field state produced by a full cycle of quantum Rabi oscillation. The dephasing angle, conditioned to the initial atom-field state, can be adjusted over a wide range by tuning the atom-cavity frequency difference. We demonstrate that the gate preserves qubit coherence and generates entanglement. This gate is an essential tool for the nondestructive measurement of single photons and for the manipulation of many-qubit entanglement in cavity QED. PACS numbers: 03.67.Lx, 32.80.Rm, 42.50.Ar Entanglement is a most striking feature of quantum theory. Its puzzling implications have motivated an intense theoretical and experimental research work. It has been proposed to make use of many entangled two-level quantum systems (qubits) to implement new information processing functions [1]. These applications require the production of complex entangled states. Such manipulations can be decomposed into a sequence of simple unitary evolutions, involving one or two qubits, performed by quantum gates.
We have built a microwave Fabry-Perot resonator made of diamond-machined copper mirrors coated wi... more We have built a microwave Fabry-Perot resonator made of diamond-machined copper mirrors coated with superconducting niobium. Its damping time (Tc = 130 ms at 51 GHz and 0.8 K) corresponds to a finesse of 4.6 x 109, the highest ever reached for a Fabry-Perot in any frequency range. This result opens novel perspectives for quantum information, decoherence and non-locality studies.
Physical Review Letters, 2001
Following a recent proposal by S. B. Zheng and G. C. Guo (Phys. Rev. Lett. 85, 2392 (2000)), we r... more Following a recent proposal by S. B. Zheng and G. C. Guo (Phys. Rev. Lett. 85, 2392 (2000)), we report an experiment in which two Rydberg atoms crossing a non-resonant cavity are entangled by coherent energy exchange. The process, mediated by the virtual emission and absorption of a microwave photon, is characterized by a collision mixing angle four orders of magnitude larger than for atoms colliding in free space with the same impact parameter. The final entangled state is controlled by adjusting the atom-cavity detuning. This procedure, essentially insensitive to thermal fields and to photon decay, opens promising perspectives for complex entanglement manipulations.
Nature, 2001
To illustrate the quantum mechanical principle of complementarity, Bohr described an interferomet... more To illustrate the quantum mechanical principle of complementarity, Bohr described an interferometer with a microscopic slit that records the particle's path. Recoil of the quantum slit causes it to become entangled with the particle, resulting in a kind of Einstein-Podolsky-Rosen pair. As the motion of the slit can be observed, the ambiguity of the particle's trajectory is lifted, suppressing interference effects. In contrast, the state of a sufficiently massive slit does not depend on the particle's path; hence, interference fringes are visible. Although many experiments illustrating various aspects of complementarity have been proposed and realized, none has addressed the quantum-classical limit in the design of the interferometer. Here we report an experimental investigation of complementarity using an interferometer in which the properties of one of the beam-splitting elements can be tuned continuously from being effectively microscopic to macroscopic. Following a recent proposal, we use an atomic double-pulse Ramsey interferometer, in which microwave pulses act as beam-splitters for the quantum states of the atoms. One of the pulses is a coherent field stored in a cavity, comprising a small, adjustable mean photon number. The visibility of the interference fringes in the final atomic state probability increases with this photon number, illustrating the quantum to classical transition.
We have performed multiparticle entanglement experiments with circular Rydberg atoms crossing one... more We have performed multiparticle entanglement experiments with circular Rydberg atoms crossing one at a time a high Q superconducting microwave cavity. Two-level atoms and a zero or one photon field stored in the cavity act as qubits carrying quantum information. Controlled qubit entanglement is produced by the quantum Rabi oscillation coupling the atom to the cavity field. Qubit state superpositions
Physical Review A, 2001
Using a single circular Rydberg atom, we have prepared two modes of a superconducting cavity in a... more Using a single circular Rydberg atom, we have prepared two modes of a superconducting cavity in a maximally entangled state. The two modes share a single photon. This entanglement is revealed by a second atom probing, after a delay, the correlations between the two modes. This experiment opens interesting perspectives for quantum information manipulation and fundamental tests of quantum theory.
Bohr, in his famous discussion with Einstein on complementarity, has stressed that the nature - q... more Bohr, in his famous discussion with Einstein on complementarity, has stressed that the nature - quantum or classical - of the interferometer parts plays an essential role to account for the fringes visibility. We have performed a Ramsey interferometry experiment with very excited Rydberg atoms, in which one "beam splitting" element is a classical field and the other - a small field stored in a superconducting cavity - continuously evolves from a microscopic quantum device into a macroscopic classical system. When microscopic, it records an unambiguous information on the atomic "path" in the interferometer and no fringes show up. When classical, it is not changed by the interaction with the atom and Ramsey fringes are observed. This experiment illustrates the complementarity concept and its intimate link with the notion of entanglement. It sheds light on the quantum-classical boundary in fundamental measurement processes.
Nature, 1999
Light detection is usually a destructive process, in that detectors annihilate photons and conver... more Light detection is usually a destructive process, in that detectors annihilate photons and convert them into electrical signals, making it impossible to see a single photon twice. But this limitation is not fundamentalÐquantum non-demolition strategies 1±3 permit repeated measurements of physically observable quantities, yielding identical results. For example, quantum non-demolition measurements of light intensity have been demonstrated 4±14 , suggesting possibilities for detecting weak forces and gravitational waves 3 . But such experiments, based on nonlinear optics, are sensitive only to macroscopic photon¯uxes. The non-destructive measurement of a single photon requires an extremely strong matter±radiation coupling; this can be realized in cavity quantum electrodynamics 15 , where the strength of the interaction between an atom and a photon can overwhelm all dissipative couplings to the environment. Here we report a cavity quantum electrodynamics experiment in which we detect a single photon non-destructively. We use atomic interferometry to measure the phase shift in an atomic wavefunction, caused by a cycle of photon absorption and emission. Our method amounts to a restricted quantum non-demolition measurement which can be applied only to states containing one or zero photons. It may lead to quantum logic gates 16 based on cavity quantum electrodynamics, and multi-atom entanglement 17 .
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Papers by stefano osnaghi