6 research outputs found
Evaluation of nitrogen- and silicon-vacancy defect centres as single photon sources in quantum key distribution
We demonstrate a quantum key distribution (QKD) testbed for room temperature
single photon sources based on defect centres in diamond. A BB84 protocol over
a short free-space transmission line is implemented. The performance of
nitrogen-vacancy (NV) as well as silicon-vacancy defect (SiV) centres is
evaluated and an extrapolation for next-generation sources with enhanced
efficiency is discussed.Comment: 14 pages, 5 figure
Autonomous Maxwell's demon in a cavity QED system
We present an autonomous Maxwell's demon scheme. It is first analysed
theoretically in term of information exchange in a closed system and then
implemented experimentally with a single Rydberg atom and a high-quality
microwave resonator. The atom simulates both a qubit interacting with the
cavity, and a demon carrying information on the qubit state. While the cold
qubit crosses the hot cavity, the demon prevents energy absorption from the
cavity mode, apparently violating the second law of thermodynamics. Taking into
account the change of the mutual information between the demon and the
qubit-cavity system gives rise to a generalized expression of the second law
that we establish and measure. Finally, considering the closed
qubit-cavity-demon system, we establish and measure that the generalized second
law can be recast into an entropy conservation law, as expected for a unitary
evolution.Comment: 6 pages, 3 figure
Trajectory tomography of delocalized states of two microwave cavities
La reconstruction d'Ă©tats quantiques, ou tomographie, joue un rĂŽle central dans les technologies quantiques, afin de caractĂ©riser les opĂ©rations effectuĂ©es et d'extraire de l'information sur les Ă©tats rĂ©sultats de traitements d'information quantique. Les mĂ©thodes rĂ©pandues de tomographie reposent gĂ©nĂ©ralement sur des mesures idĂ©ales, effectuĂ©es une seule fois sur chaque prĂ©paration de l'Ă©tat d'intĂ©rĂȘt. Dans ce travail, nous utilisons une nouvelle mĂ©thode, appelĂ©e tomographie par trajectoires, qui consiste Ă enregistrer, pour chaque rĂ©alisation de l'Ă©tat, la trajectoire quantique suivie par le systĂšme Ă l'aide d'une sĂ©rie de mesures successives du systĂšme, en prĂ©sence d'imperfections expĂ©rimentales et de dĂ©cohĂ©rence. On extrait alors plus d'information sur l'Ă©tat Ă reconstruire et on est capable, Ă partir d'un ensemble de mesures accessibles donnĂ©es, de crĂ©er des mesures plus gĂ©nĂ©rales. Ă l'aide des techniques de l'Ă©lectrodynamique quantique en cavitĂ©, nous avons prĂ©parĂ© des Ă©tats intriquĂ©s de photons micro-onde dĂ©localisĂ©s sur deux modes distants. Nous avons ensuite reconstruit ces Ă©tats par tomographie par trajectoires, dans un espace de Hilbert de grande dimension. Nous montrons que cette mĂ©thode permet de reconstruire l'Ă©tat, de dĂ©velopper des stratĂ©gies de mesure adaptĂ©es pour accĂ©lĂ©rer l'extraction d'information sur les cohĂ©rences quantiques d'intĂ©rĂȘt et qu'elle fournit une estimation de l'incertitude sur les coefficients de la matrice densitĂ© reconstruite.Quantum state estimation, or tomography, is a key component of quantum technologies, allowing to characterise quantum operations and to extract information on the results of quantum information processes. The usual tomography techniques rely on ideal, single-shot measurements of the unknown state. In this work, we use a new approach, called trajectory quantum tomography, where the quantum trajectory of each realization of the state is recorded through a series of measurements, including experimental imperfections and decoherence. This strategy increases the extracted amount of information and allows to build new measurements for a set of feasible measurements.Using the tools of cavity quantum eletrodynamics, we have prepared entangled states of microwave photons spread on two separated modes. We have then performed a trajectory tomography of these states, in a large Hilbert space. We have proved that this method allows to estimate the state, to develop faster strategies for extracting information on specific coherences of the state and to compute error bars on the components of the estimated density matrix
Tomographie par trajectoires d'états délocalisés du champ micro-onde de deux cavités
Quantum state estimation, or tomography, is a key component of quantum technologies, allowing to characterise quantum operations and to extract information on the results of quantum information processes. The usual tomography techniques rely on ideal, single-shot measurements of the unknown state. In this work, we use a new approach, called trajectory quantum tomography, where the quantum trajectory of each realization of the state is recorded through a series of measurements, including experimental imperfections and decoherence. This strategy increases the extracted amount of information and allows to build new measurements for a set of feasible measurements.Using the tools of cavity quantum eletrodynamics, we have prepared entangled states of microwave photons spread on two separated modes. We have then performed a trajectory tomography of these states, in a large Hilbert space. We have proved that this method allows to estimate the state, to develop faster strategies for extracting information on specific coherences of the state and to compute error bars on the components of the estimated density matrix.La reconstruction d'Ă©tats quantiques, ou tomographie, joue un rĂŽle central dans les technologies quantiques, afin de caractĂ©riser les opĂ©rations effectuĂ©es et d'extraire de l'information sur les Ă©tats rĂ©sultats de traitements d'information quantique. Les mĂ©thodes rĂ©pandues de tomographie reposent gĂ©nĂ©ralement sur des mesures idĂ©ales, effectuĂ©es une seule fois sur chaque prĂ©paration de l'Ă©tat d'intĂ©rĂȘt. Dans ce travail, nous utilisons une nouvelle mĂ©thode, appelĂ©e tomographie par trajectoires, qui consiste Ă enregistrer, pour chaque rĂ©alisation de l'Ă©tat, la trajectoire quantique suivie par le systĂšme Ă l'aide d'une sĂ©rie de mesures successives du systĂšme, en prĂ©sence d'imperfections expĂ©rimentales et de dĂ©cohĂ©rence. On extrait alors plus d'information sur l'Ă©tat Ă reconstruire et on est capable, Ă partir d'un ensemble de mesures accessibles donnĂ©es, de crĂ©er des mesures plus gĂ©nĂ©rales. Ă l'aide des techniques de l'Ă©lectrodynamique quantique en cavitĂ©, nous avons prĂ©parĂ© des Ă©tats intriquĂ©s de photons micro-onde dĂ©localisĂ©s sur deux modes distants. Nous avons ensuite reconstruit ces Ă©tats par tomographie par trajectoires, dans un espace de Hilbert de grande dimension. Nous montrons que cette mĂ©thode permet de reconstruire l'Ă©tat, de dĂ©velopper des stratĂ©gies de mesure adaptĂ©es pour accĂ©lĂ©rer l'extraction d'information sur les cohĂ©rences quantiques d'intĂ©rĂȘt et qu'elle fournit une estimation de l'incertitude sur les coefficients de la matrice densitĂ© reconstruite
Benchmarking Maximum-Likelihood State Estimation with an Entangled Two-Cavity State
3 figures, Supplementary informationInternational audienceThe efficient quantum state reconstruction algorithm described in [P. Six et al., Phys. Rev. A 93, 012109 (2016)] is experimentally implemented on the non-local state of two microwave cavities entangled by a circular Rydberg atom. We use information provided by long sequences of measurements performed by resonant and dispersive probe atoms over time scales involving the system decoherence. Moreover, we benefit from the consolidation, in the same reconstruction, of different measurement protocols providing complementary information. Finally, we obtain realistic error bars for the matrix elements of the reconstructed density operator. These results demonstrate the pertinence and precision of the method, directly applicable to any complex quantum system