Comment on "Secure direct communication with a quantum one-time pad"

In the paper [Phys. Rev. A \textbf{69}, 052319 (2004)], a quantum direct communication protocol is proposed which is claimed to be unconditionally secure even for the case of a noisy channel. We show that this is not the case by giving an undetectable attack scheme

Secure direct communication using entanglement

A novel communication protocol based on an entangled pair of qubits is presented, allowing secure direct communication from one party to another without the need for a shared secret key. Since the information is transferred in a deterministic manner, no qubits have to be discarded and every qubit carries message information. The security of the transfer against active and passive eavesdropping attacks is provided. The detection rate of active attacks is at least 25%. The protocol works with a quantum efficiency of 1 bit per qubit transmitted.Comment: 4 pages, 5 figures, REVTE

„Nur näher kommt, Ihr wunderschönen Masken“ – Adolph Menzels Maskensouper

Menzels wenig bekannte Gouache Maskensouper von 1855 stellt motivisch den Nukleus der Werkgruppe seiner „Ballbilder“ dar und zeugt von Menzels Begeisterung für das Musiktheater. Bei eingehender Betrachtung kann man im Maskensouper die Variation einer Szene aus Mozarts Don Giovanni erkennen. Eine bislang motivisch unidentifizierte Zeichnung im Berliner Kupferstichkabinett, die einen Spiegel im Potsdamer Neuen Palais zeigt, diente als Vorlage zu dieser Gouache. In seiner Komposition nimmt das Maskensouper die Dreiteilung im 1856 geschaffenen Théâtre du Gymnase vorweg. Die Verbindung von perspektivischer Raumkonstruktion und atmosphärischer Schilderung belegt Menzels Hinwendung zum Realismus im Jahr vor seinem ersten großen Publikumserfolg mit dem Bild Friedrich II. und die Seinen bei Hochkirch

Natural convection in high temperature flat plate latent heat thermal energy storage systems

The impact of natural convection on melting in high temperature flat plate latent heat thermal energy storage systems is studied with an experimentally validated numerical model in a parameter study with various widths and heights of enclosure dimensions. The storage material is the eutectic mixture of sodium nitrate and potassium nitrate (KNO3-NaNO3). The investigated half widths of the rectangular enclosures between two heated vertical flat plates are 5, 10 and 25 mm; their heights are 25, 50, 100, 200, 500 and 1000 mm. These parameters result in low to very high aspect ratios between 0.5 and 40 and Rayleigh numbers between 1.2 · 10^4 and 1.6 · 10^6. The results are evaluated by dimensional analysis to find general dependencies between enclosure dimensions and natural convection occurrence and strength. To assess the influence of natural convection on the heat transfer enhancement, the convective enhancement factor is introduced. This non-dimensional number is defined as the ratio of actual heat flux by natural convection to a hypothetical heat flux by conduction only. The central findings of the present work are correlations for the mean convective enhancement factor and the critical liquid phase fraction for natural convection onset that are valid for a wide parameter range. The results indicate that heat transfer enhancement due to natural convection increases with greater widths and smaller heights of storage material enclosures. Hence, the vertical segmentation of high enclosures into smaller ones should be considered to enhance heat transfer during charging

Natural convection melting in a high temperature flat plate latent heat storage system: Parameter study of enclosure dimensions

The impact of natural convection melting in a high temperature flat plate latent heat thermal energy storage system is studied numerically. The storage material is the eutectic mixture of sodium nitrate and potassium nitrate (KNO3-NaNO3). A parameter study on storage material enclosure dimensions is conducted for various widths and heights. Low to very high aspect ratios between 0.5 and 40 and Rayleigh numbers from 1.2·10^4 to 1.6·10^6 are obtained. The liquid phase fraction evolution with time is scaled to non-dimensional form and the impact of natural convection on the heat flux is shown with a convective enhancement factor that is the ratio of heat flux to a hypothetical heat flux only by conduction. The results can be used for future design optimizations considering the effect of natural convection

Lossless quantum data compression and variable-length coding

In order to compress quantum messages without loss of information it is necessary to allow the length of the encoded messages to vary. We develop a general framework for variable-length quantum messages in close analogy to the classical case and show that lossless compression is only possible if the message to be compressed is known to the sender. The lossless compression of an ensemble of messages is bounded from below by its von-Neumann entropy. We show that it is possible to reduce the number of qbits passing through a quantum channel even below the von-Neumann entropy by adding a classical side-channel. We give an explicit communication protocol that realizes lossless and instantaneous quantum data compression and apply it to a simple example. This protocol can be used for both online quantum communication and storage of quantum data.Comment: 16 pages, 5 figure

Toward the multiphoton parametric oscillators

We propose novel types of parametric oscillators generating both three-photon and four-photon bright light which are accessible for an experiment. The devices are based on the cascaded down-conversion processes and consist of second-order media inserted in two-resonant mode cavity. Discussion of dissipation and quantum features of the system are performed by the quantum-jump simulation method and concerns to the Wigner functions. The phase-space multistabilities and critical threshold behavior of three- and four-photon subharmonics are obtained.Comment: 3 figures, submitted to Physics Letter