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In this letter, a broadband radar cross section (RCS) reduction binary metasurface with a high-efficiency intraband transmission window is proposed and implemented based on multilayered elements combining the Jerusalem cross and cross-slot patterns. Electromagnetic responses of such structures are investigated by the equivalent circuit method. The results indicate that the metasurface consisting of elements with two types of Jerusalem crosses can invoke diffused scattering to reduce the RCS of metallic targets. Meanwhile, the metasurface has a high-efficiency transmission window since the bandpass cross-slot pattern is deployed here. The simulation results indicate that the metasurface can achieve a −10 dB RCS reduction from 3.5 to 11.5 GHz and transmission with an insertion loss of 0.72 dB at 8.4 GHz. The performances of the proposed metasurface are verified experimentally. Our design may find potential applications in the low-RCS antenna or the stealth radome for wireless facilities. [ABSTRACT FROM AUTHOR]

We give the first systematic study on the second order asymptotics of the operational task of coherence distillation with and without assistance. In the unassisted setting, we introduce a variant of randomness extraction framework where free incoherent operations are allowed before the incoherent measurement and the randomness extractors. We then show that the maximum number of random bits extractable from a given quantum state is precisely equal to the maximum number of coherent bits distillable from the same state. This relation enables us to derive tight second order expansions of both tasks in the independent and identically distributed setting. Remarkably, the incoherent operation classes that can empower coherence distillation for generic states all admit the same second order expansions, indicating their operational equivalence for coherence distillation in both asymptotic and large block length regimes. We then generalize the above line of research to the assisted setting, arising naturally in bipartite quantum systems where Bob distills coherence from the state at hand, aided by the benevolent Alice possessing the other system. More precisely, we introduce a new assisted incoherent randomness extraction task and establish an exact relation between this task and the assisted coherence distillation. It strengthens the one-shot relation in the unassisted setting and confirms that this cryptographic framework offers a new perspective to the study of quantum coherence distillation. Likewise, this relation yields second order characterizations to the assisted tasks. As by-products, we show the strong converse property of the tasks above from their second order expansions. [ABSTRACT FROM AUTHOR]

We study the general framework of quantum channel simulation, that is, the ability of a quantum channel to simulate another one using different classes of codes. First, we show that the minimum error of simulation and the one-shot quantum simulation cost under no-signalling assisted codes are given by semidefinite programs. Second, we introduce the channel’s smooth max-information, which can be seen as a one-shot generalization of the mutual information of a quantum channel. We provide an exact operational interpretation of the channel’s smooth max-information as the one-shot quantum simulation cost under no-signalling assisted codes, which significantly simplifies the study of channel simulation and provides insights and bounds for the case under entanglement-assisted codes. Third, we derive the asymptotic equipartition property of the channel’s smooth max-information; i.e., it converges to the quantum mutual information of the channel in the independent and identically distributed asymptotic limit. This implies the quantum reverse Shannon theorem in the presence of no-signalling correlations. Finally, we explore the simulation cost of various quantum channels. [ABSTRACT FROM AUTHOR]

Entanglement distillation, an essential quantum information processing task, refers to the conversion from multiple copies of noisy entangled states to a smaller number of highly entangled states. In this paper, we study the non-asymptotic fundamental limits for entanglement distillation. We investigate the optimal tradeoff between the distillation rate, the number of prepared states, and the error tolerance. First, we derive the one-shot distillable entanglement under completely positive partial transpose preserving operations as a semidefinite program and demonstrate an exact characterization via the quantum hypothesis testing relative entropy. Second, we establish efficiently computable second-order estimations of the distillation rate for general quantum states. In particular, we provide explicit as well as approximate evaluations for various quantum states of practical interest, including pure states, mixture of Bell states, maximally correlated states, and isotropic states. [ABSTRACT FROM AUTHOR]

We explore several new converse bounds for classical communication over quantum channels in both the one-shot and asymptotic regimes. First, we show that the Matthews-Wehner meta-converse bound for entanglement-assisted classical communication can be achieved by activated, no-signaling assisted codes, suitably generalizing a result for classical channels. Second, we derive a new efficiently computable meta-converse on the amount of classical information unassisted codes can transmit over a single use of a quantum channel. As applications, we provide a finite resource analysis of classical communication over quantum erasure channels, including the second-order and moderate deviation asymptotics. Third, we explore the asymptotic analogue of our new meta-converse, the $\Upsilon $ -information of the channel. We show that its regularization is an upper bound on the classical capacity, which is generally tighter than the entanglement-assisted capacity and other known efficiently computable strong converse bounds. For covariant channels, we show that the $\Upsilon $ -information is a strong converse bound. [ABSTRACT FROM AUTHOR]

We derive several efficiently computable converse bounds for quantum communication over quantum channels in both the one-shot and asymptotic regime. First, we derive one-shot semidefinite programming (SDP) converse bounds on the amount of quantum information that can be transmitted over a single use of a quantum channel, which improve the previous bound from [Tomamichel/Berta/Renes, Nat. Commun. 7, 2016]. As applications, we study quantum communication over depolarizing channels and amplitude damping channels with finite resources. Second, we find an SDP-strong converse bound for the quantum capacity of an arbitrary quantum channel, which means the fidelity of any sequence of codes with a rate exceeding this bound will vanish exponentially fast as the number of channel uses increases. Furthermore, we prove that the SDP-strong converse bound improves the partial transposition bound introduced by Holevo and Werner. Third, we prove that this SDP strong converse bound is equal to the so-called max-Rains information, which is an analog to the Rains information introduced in [Tomamichel/Wilde/Winter, IEEE Trans. Inf. Theory 63:715, 2017]. Our SDP strong converse bound is weaker than the Rains information, but it is efficiently computable for general quantum channels. [ABSTRACT FROM AUTHOR]

Low-temperature Ag sintering provides a lead-free die attachment method that is compatible with high-temperature (300 °C) power electronics applications. The reliability of sintered Ag die attach for Si and SiC die has been studied on both thick film substrates for lower current power applications and direct bond copper (DBC) substrates for higher current power applications. Pressureless and low-pressure sintering were evaluated. Sintering with low pressure yielded lower porosity (15–17%) versus pressureless sintering (∼30%). Reliability was evaluated with thermal aging (300 °C) and thermal cycling (–55 °C to + 300 °C) tests. Reliable Ag sintered die attach was achieved with assemblies having Ag-bearing surface finishes on both the die and the substrate. In contrast, the shear strength after 300 °C aging was greatly reduced when Au metallization was used either on the die or on substrate surface. In some cases, low-pressure sintering delayed the failure of the sintered Ag die attach to Au surfaces when aged at 300 °C compared to the pressureless sintering. The reliability with Pd-containing substrate metallizations was intermediate between Ag and Au metallizations. The thermal cycle reliability on DBC substrates was limited by failure at the Cu-to-alumina interface over the wide temperature range, while on the thick film substrates high adhesion was maintained after 1000 thermal cycles. [ABSTRACT FROM PUBLISHER]

A thin-film multichip module technology has been developed and evaluated for packaging high-temperature (300 °C) geothermal well instrumentation. Since a measurement-while-drilling tool is exposed to a combination of high-temperature and shock/vibration loading, flip-chip technology was selected to avoid vibration-related problems with bond wires. Thermocompression flip-chip bonding was characterized in thermal aging, thermal cycling, and thermal shock/vibration tests. Three digital circuit boards were fabricated and electrical characteristics of the digital circuit boards were evaluated. The experimental results show that thin-film substrates combined with flip-chip assembly are a viable approach for fabrication of digital circuit boards for use in extreme environments. [ABSTRACT FROM AUTHOR]

A thin-film multichip module substrate technology has been developed and evaluated for packaging high-temperature (300 °C) geothermal well instrumentation. The base substrate technology selected was AlN to minimize the difference in the coefficient of thermal expansion between the substrate and the SiC digital die. The conductor was vacuum deposited Ti/Ti:W/Au followed by an electroplated Au. A plasma-enhanced chemical vapor-deposited silicon nitride was used for the interlayer dielectric. The substrate was characterized as a function of temperature and after aging at 300 °C. The electrical properties and adhesion remained stable after 2000 h at 300 °C. [ABSTRACT FROM AUTHOR]