Alessandro Zavatta

Probing Quantum Commutation Rules by Addition and Subtraction of Single Photons to/from a Light Field

The possibility of arbitrarily “adding” and “subtracting” single photons to and from a light field may give access to a complete engineering of quantum states and to fundamental quantum phenomena. We experimentally implemented simple alternated sequences of photon creation and annihilation on a thermal field and used quantum tomography to verify the peculiar character of the resulting light states. In particular, as the final states depend on the order in which the two actions are performed, we directly observed the noncommutativity of the creation and annihilation operators, one of the cardinal concepts of quantum mechanics, at the basis of the quantum behavior of light. These results represent a step toward the full quantum control of a field and may provide new resources for quantum information protocols.

Single-photon excitation of a coherent state : Catching the elementary step of stimulated light emission

When a single quantum of electromagnetic field excitation is added to the same spatiotemporal mode of a coherent state, a new field state is generated that exhibits intermediate properties between those of the two parents. Such a single-photon-added coherent state is obtained by the action of the photon creation operator on a coherent state and can thus be regarded as the result of the most elementary excitation process of a classical light field. Here we present and describe in depth the experimental realization of such states and their complete analysis by means of a novel ultrafast, time-domain, quantum homodyne tomography technique clearly revealing their nonclassical character.

Experimental nonclassicality of single-photon-added thermal light states

We report the experimental realization and tomographic analysis of quantum light states obtained by exciting a classical thermal field by a single photon. Such states, although completely incoherent, possess a tunable degree of quantumness which is here exploited to put to a stringent experimental test some of the criteria proposed for the proof and the measurement of state nonclassicality. The quantum character of the states is also given in quantum information terms by evaluating the amount of entanglement that they can produce.

A high-fidelity noiseless amplifier for quantum light states

Researchers demonstrate a probabilistic noiseless linear amplifier based on photon addition and subtraction. The technique enables coherent states to be amplified to the highest levels of effective gain and final-state fidelity, and could become an essential tool for applications in quantum communication and metrology.

Generation of hybrid entanglement of light

Hyunseok Jeong, Alessandro Zavatta, Minsu Kang, Seung-Woo Lee, Luca S. Costanzo, Samuele Grandi, Timothy C. Ralph & Marco Bellini Center for Macroscopic Quantum Control, Department of Physics and Astronomy, Seoul National University, Seoul, 151-742, Korea Istituto Nazionale di Ottica (INO-CNR), L.go E. Fermi 6, 50125 Florence, Italy LENS and Department of Physics, University of Firenze, 50019 Sesto Fiorentino, Florence, Italy Centre for Quantum Computation and Communication Technology, School of Mathematics and Physics, University of Queensland, Qld 4072, Australia.

Experimental Demonstration of the Bosonic Commutation Relation via Superpositions of Quantum Operations on Thermal Light Fields

We present the experimental realization of a scheme, based on single-photon interference, for implementing superpositions of distinct quantum operations. Its application to a thermal light field (a well-categorized classical entity) illustrates quantum superposition from a new standpoint and provides a direct and quantitative verification of the bosonic commutation relation between creation and annihilation operators. By shifting the focus towards operator superpositions, this result opens interesting alternative perspectives for manipulating quantum states.

Scheme for proving the bosonic commutation relation using single-photon interference.

We propose an experiment to directly prove the commutation relation between bosonic annihilation and creation operators, based on the recent experimental success in single-photon subtraction and addition. We devise a single-photon interferometer to realize coherent superpositions of two sequences of photon addition and subtraction. Depending on the interference outcome, the commutation relation is directly proven or a highly nonclassical state is produced. Experimental imperfections are assessed to show that the realization of the scheme is highly feasible.

Subtracting photons from arbitrary light fields: experimental test of coherent state invariance by single-photon annihilation

The operator annihilating a single quantum of excitation in a bosonic field is one of the cornerstones for the interpretation and prediction of the behavior of the microscopic quantum world. Here we present a systematic experimental study of the effects of single-photon annihilation on some paradigmatic light states. In particular, by demonstrating the invariance of coherent states by this operation, we provide the first direct verification of their definition as eigenstates of the photon annihilation operator.

Time-domain analysis of quantum states of light: noise characterization and homodyne tomography

We measured the time-domain quantum statistics of a pulsed, high-repetition-rate optical field by balanced homodyne detection. The measuring apparatus discriminates the time scales on which intrinsic quantum fluctuations prevail from those scales for which technical noise is overwhelming. A tomographic reconstruction of weak coherent states with various average photon numbers demonstrates the potential ability of the system to measure high-repetition-rate, time-resolved signals. Possible extensions to other physical situations are discussed.

Towards higher precision and operational use of optical homodyne tomograms

We present the results of an operational use of experimentally measured optical tomograms to determine state characteristics (purity) avoiding any reconstruction of quasiprobabilities. We also develop a natural way how to estimate the errors (including both statistical and systematic ones) by an analysis of the experimental data themselves. Precision of the experiment can be increased by postselecting the data with minimal (systematic) errors. We demonstrate those techniques by considering coherent and photon-added coherent states measured via the time-domain improved homodyne detection. The operational use and precision of the data allowed us to