Quantum Rabi oscillations in coherent and in mesoscopic "cat" field states

International audienceThe simple resonant Rabi oscillation of a two-level system in a single-mode coherent field reveals complex features at the mesoscopic scale, with oscillation collapses and revivals. Using slow circular Rydberg atoms interacting with a superconducting microwave cavity, we explore this phenomenon in an unprecedented range of interaction times and photon numbers. We demonstrate the efficient production of 'cat' states, quantum superposition of coherent components with nearly opposite phases and sizes in the range of few tens of photons. We measure cuts of their Wigner functions revealing their quantum coherence and observe their fast decoherence. This experiment opens promising perspectives for the rapid generation and manipulation of non-classical states in cavity and circuit Quantum Electrodynamics

Determining the Quantum Expectation Value by Measuring a Single Photon

Quantum mechanics, one of the keystones of modern physics, exhibits several peculiar properties, differentiating it from classical mechanics. One of the most intriguing is that variables might not have definite values. A complete quantum description provides only probabilities for obtaining various eigenvalues of a quantum variable. These and corresponding probabilities specify the expectation value of a physical observable, which is known to be a statistical property of an ensemble of quantum systems. In contrast to this paradigm, we demonstrate a unique method allowing to measure the expectation value of a physical variable on a single particle, namely, the polarisation of a single protected photon. This is the first realisation of quantum protective measurements.Comment: Nature Physics, in press (this version corresponds to the one initially submitted to Nature Physics

Fast as a shadow, expressive as a tree: Optimized memory monitoring for C

International audienceOne classical approach to ensuring memory safety of C programs is based on storing block metadata in a tree-like datastructure. However it becomes relatively slow when the number of memory locations in the tree becomes high. Another solution, based on shadow memory, allows very fast constant-time access to metadata and led to development of several highly optimized tools for the detection of memory safety errors. However, this solution appears to be insufficient for evaluation of complex memory-related properties of an expressive specification language. In this work, we address memory monitoring in the context of runtime assertion checking of C programs annotated in E-ACSL, an expressive specification language offered by the FRAMA-C framework for the analysis of C code. We present an original combination of a tree-based and a shadow-memory-based techniques that reconciles the efficiency of shadow memory and the higher expressiveness of annotations that can be evaluated using a tree of metadata. Shadow memory with its instant access to stored metadata is used whenever small shadow metadata suffices to evaluate required annotations, while richer metadata stored in a compact prefix tree (Patricia trie) is used for evaluation of more complex memory annotations supported by E-ACSL. We also present a preliminary static analysis step that determines which variables should be monitored (and in which way) in order to be able to evaluate annotations present in the program. The combined monitoring technique and the pre-analysis step have been implemented in the runtime assertion checking tool for E-ACSL. Our initial experiments confirm that the proposed hybrid approach leads to a significant speedup with respect to an earlier implementation based on a Patricia trie alone without any loss of precision, while the proposed static analysis reduces the monitoring of irrelevant variables and further improves the performances of the instrumented code

Fast as a shadow, expressive as a tree: Hybrid memory monitoring for C.

Conference of 30th Annual ACM Symposium on Applied Computing, SAC 2015 ; Conference Date: 13 April 2015 Through 17 April 2015; Conference Code:117701International audienceOne classical approach to ensuring memory safety of C programs is based on storing block metadata in a tree-like datastructure. However it becomes relatively slow when the number of memory locations in the tree becomes high. Another solution, based on shadow memory, allows very fast constant-time access to metadata and led to development of several highly optimized tools for detection of memory safety errors. However, this solution appears to be insufficient for evaluation of complex memory-related properties of an expressive specification language. In this work, we address memory monitoring in the context of runtime assertion checking of C programs annotated in E-ACSL, an expressive specification language offered by the FRAMA-C framework for analysis of C code. We present an original combination of a tree-based and a shadow-memory-based techniques that reconciles both the efficiency of shadow memory with the higher expressiveness of annotations whose runtime evaluation can be ensured by a tree of metadata. Shadow memory with its instant access to stored metadata is used whenever small shadow metadata suffices to evaluate required annotations, while richer metadata stored in a compact prefix tree (Patricia trie) is used for evaluation of more complex memory annotations supported by E-ACSL. This combined monitoring technique has been implemented in the runtime assertion checking tool for E-ACSL. Our initial experiments confirm that the proposed hybrid approach leads to a significant speedup with respect to an earlier implementation based on a Patricia trie alone without any loss of precision