Rates of Multipartite Entanglement Transformations.

The theory of the asymptotic manipulation of pure bipartite quantum systems can be considered completely understood: the rates at which bipartite entangled states can be asymptotically transformed into each other are fully determined by a single number each, the respective entanglement entropy. In the multipartite setting, similar questions of the optimally achievable rates of transforming one pure state into another are notoriously open. This seems particularly unfortunate in the light of the revived interest in such questions due to the perspective of experimentally realizing multipartite quantum networks. In this Letter, we report substantial progress by deriving simple upper and lower bounds on the rates that can be achieved in asymptotic multipartite entanglement transformations. These bounds are based on ideas of entanglement combing and state merging. We identify cases where the bounds coincide and hence provide the exact rates. As an example, we bound rates at which resource states for the cryptographic scheme of quantum secret sharing can be distilled from arbitrary pure tripartite quantum states. This result provides further scope for quantum internet applications, supplying tools to study the implementation of multipartite protocols over quantum networks.

Entanglement and Coherence in Quantum State Merging.

Understanding the resource consumption in distributed scenarios is one of the main goals of quantum information theory. A prominent example for such a scenario is the task of quantum state merging, where two parties aim to merge their tripartite quantum state parts. In standard quantum state merging, entanglement is considered to be an expensive resource, while local quantum operations can be performed at no additional cost. However, recent developments show that some local operations could be more expensive than others: it is reasonable to distinguish between local incoherent operations and local operations which can create coherence. This idea leads us to the task of incoherent quantum state merging, where one of the parties has free access to local incoherent operations only. In this case the resources of the process are quantified by pairs of entanglement and coherence. Here, we develop tools for studying this process and apply them to several relevant scenarios. While quantum state merging can lead to a gain of entanglement, our results imply that no merging procedure can gain entanglement and coherence at the same time. We also provide a general lower bound on the entanglement-coherence sum and show that the bound is tight for all pure states. Our results also lead to an incoherent version of Schumacher compression: in this case the compression rate is equal to the von Neumann entropy of the diagonal elements of the corresponding quantum state.

Assisted Distillation of Quantum Coherence.

We introduce and study the task of assisted coherence distillation. This task arises naturally in bipartite systems where both parties work together to generate the maximal possible coherence on one of the subsystems. Only incoherent operations are allowed on the target system, while general local quantum operations are permitted on the other; this is an operational paradigm that we call local quantum-incoherent operations and classical communication. We show that the asymptotic rate of assisted coherence distillation for pure states is equal to the coherence of assistance, an analog of the entanglement of assistance, whose properties we characterize. Our findings imply a novel interpretation of the von Neumann entropy: it quantifies the maximum amount of extra quantum coherence a system can gain when receiving assistance from a collaborative party. Our results are generalized to coherence localization in a multipartite setting and possible applications are discussed.

Dynamic hole burning within special pair absorption band of Rhodobacter sphaeroides (R-26) reaction center at room temperature.

The absorbance spectrum of reaction centers of Rhodobacter sphaeroides at room temperature consists of relatively narrow spectral components which are moving in the femtosecond time scale and can be bleached by femtosecond laser pulses in the short wavelength region with a subsequent broadening and red shift of the bleaching (time constant approximately 250 fs). These data are discussed in terms of the population of the vibronic wave packets in the ground state by the interaction with phonons at 293K. The motion of these packets is probably responsible for the absorbance spectrum of the primary electron donor P at 293K with enhanced short wavelength components and with suppressed Stokes components.

Femtosecond kinetics of electron transfer in the bacteriochlorophyll(M)-modified reaction centers from Rhodobacter sphaeroides (R-26).

Formation of the vibronic wavepacket by 90-fs excitation of the primary electron donor P in bacteriochlorophyll(M)-modified reaction centers is shown to induce nuclear motions accompanied by (1) oscillation of the stimulated emission from excited primary electron donor P* and (2) wavepacket motions leading to electron transfer at 293 K from P* to bacteriochlorophyll (B(L)) and then to bacteriopheophytin (H(L)). The latter motions have low frequency (about 15 cm-1) and are related to protein-nuclear motions which are along the reaction coordinate. When the wavepacket approaches the intersection of the reactant (P*B(L)) and product (P+B(L)-) potential energy surfaces (approximately 1.5 ps delay), about 60% of P* is converted to the P+B(L)- state. The P+H(L)- state formation is delayed by approximately 2 ps with respect to that of P+B(L)-. It is suggested that the wavepacket is transferred to and moves also slowly on the P+B(L)- potential energy surface and approaches the intersection of the surfaces of P+B(L)- and P+H(L)- within approximately 2 ps (approximately 8 cm-1), indicating the electron transfer to H(L).

[Surgical treatment of patients with generalized atherosclerosis of the aorta and its branches]. / Khirurgicheskoe lechenie bolnykh s rasprostranënnym aterosklerozom aorty i eë vetvei.

The article analyses experience accumulated since September 1988 by the Department of Vascular Surgery based on Nizhny Novgorod Regional Clinical Hospital. The Department is equipped with apparatuses by means of which patients with generalized atherosclerotic lesions of the aorta and its branches can be examined to a full measure. The authors performed 287 operations on 205 patients with 3.9% mortality. The tactics of surgical treatment of patients with various atherosclerotic lesions of the aorta and its branches are analysed. It is concluded that multistage correction of the blood flow is most optimal in such patients.

Fabrication and analysis of a directional coupler written in glass by nanojoule femtosecond laser pulses.

A directional coupler written in a glass sample by the focused 400-nm output from a 25-fs oscillator is reported. The coupler is single mode; the splitting ratio is 1.9 dB at 633 nm. A refractive-index profile of the waveguide with a magnitude of Dn = 4.5 x 10(-3) was retrieved from a near-field mode pattern.

Femtosecond ultraviolet autocorrelation measurements based on two-photon conductivity in fused silica.

We utilize the two-photon conductivity of a fused-silica substrate to produce a photoconductive switch for use in an intensity autocorrelator for ultraviolet ultrashort pulses. We perform measurements at 267 nm with pulse durations in the range of 110-330 fs and with energies as weak as 10 nJ. Based on the bandgap of fused silica, this device can potentially operate in the wavelength range of 140-280 nm.