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Philippe Grangier

Publications and source records attributed to Philippe Grangier.

108 records · Page 6Linked to original sources
arXiv2004

Contextual objectivity and the quantum formalism

The new orthodoxy of quantum mechanics (QM) based on the decoherence approach requires many-worlds as an essential ingredient for logical consistency, and one may wonder what status to give to all these "other worlds". Here we advocate that it is possible to build a consistent approach to QM where no other worlds are needed, and where the quantum formalism appears as a consequence of requiring the enumerability of physical properties. Such a quantization hypothesis is closely related to indistinguishability, and is deeply inconsistent with classical physics.

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arXiv2004

Experimental open air quantum key distribution with a single photon source

We present a full implementation of a quantum key distribution (QKD) system with a single photon source, operating at night in open air. The single photon source at the heart of the functional and reliable setup relies on the pulsed excitation of a single nitrogen-vacancy color center in diamond nanocrystal. We tested the effect of attenuation on the polarized encoded photons for inferring longer distance performance of our system. For strong attenuation, the use of pure single photon states gives measurable advantage over systems relying on weak attenuated laser pulses. The results are in good agreement with theoretical models developed to assess QKD security.

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arXiv2004

Holographic generation of micro-trap arrays for single atoms

We have generated multiple micron-sized optical dipole traps for neutral atoms using holographic techniques with a programmable liquid crystal spatial light modulator. The setup allows the storing of a single atom per trap, and the addressing and manipulation of individual trapping sites.

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arXiv2003

Contextual objectivity and quantum holism

In our effort to restate a "realistic" approach to quantum mechanics, that would fully acknowledge that local realism is untenable, we add a few more questions and answers to the list presented in quant-ph/0203131. We also suggest to replace the very misleading wording "quantum non-locality" by "quantum holism", that conveys a much better intuitive idea of the physical content of entanglement.

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arXiv2002

Maximal Violation of Bell Inequalities using Continuous Variables Measurements

We propose a whole family of physical states that yield a violation of the Bell CHSH inequality arbitrarily close to its maximum value, when using quadrature phase homodyne detection. This result is based on a new binning process called root binning, that is used to transform the continuous variables measurements into binary results needed for the tests of quantum mechanics versus local realistic theories. A physical process in order to produce such states is also suggested. The use of high-efficiency spacelike separated homodyne detections with these states and this binning process would result in a conclusive loophole-free test of quantum mechanics.

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arXiv2002

Single photon quantum cryptography

We report the full implementation of a quantum cryptography protocol using a stream of single photon pulses generated by a stable and efficient source operating at room temperature. The single photon pulses are emitted on demand by a single nitrogen-vacancy (NV) color center in a diamond nanocrystal. The quantum bit error rate is less that 4.6% and the secure bit rate is 9500 bits/s. The overall performances of our system reaches a domain where single photons have a measurable advantage over an equivalent system based on attenuated light pulses.

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arXiv2002

Reverse reconciliation protocols for quantum cryptography with continuous variables

We introduce new quantum key distribution protocols using quantum continuous variables, that are secure against individual attacks for any transmission of the optical line between Alice and Bob. In particular, it is not required that this transmission is larger than 50 %. Though squeezing or entanglement may be helpful, they are not required, and there is no need for quantum memories or entanglement purification. These protocols can thus be implemented using coherent states and homodyne detection, and they may be more efficient than usual protocols using quantum discrete variables.

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arXiv2001

Reconstructing the formalism of quantum mechanics in the ``contextual objectivity" point of view

In a previous preprint (quant-ph/0012122) we introduced a ``contextual objectivity" formulation of quantum mechanics (QM). A central feature of this approach is to define the quantum state in physical rather than in mathematical terms, in such a way that it may be given an "objective reality". Here we use some ideas about the system dimensionality, taken from quant-ph/0101012, to propose a possible axiomatic approach to QM. In this approach the structure of QM appears as a direct consequence of the non-commutative character of the (classical geometrical) group of "knobs transformations", that relate between themselves the different positions of the measurement apparatus.

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arXiv2001

Nonclassical radiation from diamond nanocrystals

The quantum properties of the fluorescence light emitted by diamond nanocrystals containing a single nitrogen-vacancy (NV) colored center is investigated. We have observed photon antibunching with very low background light. This system is therefore a very good candidate for the production of single photon on demand. In addition, we have measured larger NV center lifetime in nanocrystals than in the bulk, in good agreement with a simple quantum electrodynamical model.

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arXiv2001

Room temperature stable single-photon source

We report on the realization of a stable solid state room temperature source for single photons. It is based on the fluorescence of a single nitrogen-vacancy (NV) color center in a diamond nanocrystal. Antibunching has been observed in the fluorescence light under both continuous and pulsed excitation. Our source delivers 2*10^4 single-photon pulses per second at an excitation repetition rate of 10 MHz. The number of two-photon pulses is reduced by a factor of five compared to strongly attenuated coherent sources.

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arXiv2001

Continuous variable quantum cryptography using coherent states

We propose several methods for quantum key distribution (QKD) based upon the generation and transmission of random distributions of coherent or squeezed states, and we show that they are are secure against individual eavesdropping attacks. These protocols require that the transmission of the optical line between Alice and Bob is larger than 50 %, but they do not rely on "non-classical" features such as squeezing. Their security is a direct consequence of the no-cloning theorem, that limits the signal to noise ratio of possible quantum measurements on the transmission line. Our approach can also be used for evaluating various QKD protocols using light with gaussian statistics.

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arXiv2001

Contextual objectivity : a realistic interpretation of quantum mechanics

An attempt is made to formulate quantum mechanics (QM) in physical rather than in mathematical terms. It is argued that the appropriate conceptual framework for QM is "contextual objectivity", which includes an objective definition of the quantum state. This point of view sheds new light on topics such as the reduction postulate and the quantum measurement process.

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arXiv2000

No-cloning theorem and teleportation criteria for quantum continuous variables

We discuss the criteria presently used for evaluating the efficiency of quantum teleportation schemes for continuous variables. Using an argument based upon the difference between 1-to-2 quantum cloning (quantum duplication) and 1-to-infinity cloning (classical measurement), we show that a fidelity value larger than 2/3 is required for successful quantum teleportation of coherent states. This value has not been reached experimentally so far.

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arXiv2000

Quantum teleportation criteria for continuous variables

We discuss the criteria presently used for evaluating the efficiency of quantum teleportation schemes for continuous variables. It is argued that the fidelity criterion used so far has some severe drawbacks, and that a fidelity value larger than 2/3 is actually required for successful quantum teleportation. This value has never been reached experimentally so far.

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arXiv2000

Single photon generation by pulsed excitation of a single dipole

The fluorescence of a single dipole excited by an intense light pulse can lead to the generation of another light pulse containing a single photon. The influence of the duration and energy of the excitation pulse on the number of photons in the fluorescence pulse is studied. The case of a two-level dipole with strongly damped coherences is considered. The presence of a metastable state leading to shelving is also investigated.

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