389 research outputs found
Effect of added salt on preformed surface nanobubbles: A scaling estimate\ud
In this paper we propose a scaling argument to quantify the role of added electrolyte salt in affecting the stability and the morphology of preformed surface nanobubbles on hydrophobic substrates like the water-OTS-silicon or the water-HOPG interfaces. The added salt controls the electric double layer formation as well as affects the zeta (ζ) potential at the air-water and solid-water interfaces. The resulting electrostatic wetting tension acts in conjunction with the air-water surface tension (analogous to electrowetting scenarios), thereby affecting the nanobubble morphologies. Weak ζ potential of the water-HOPG interface or the water-OTS-silicon interface at acidic pH ensures that the added salt will have imperceptible effect on the corresponding preformed surface nanobubbles, validating the experimental observations. However, at alkaline buffer pH for the OTS-silicon substrate, under certain system conditions, salt-induced ζ potential can be substantially high so that the properties of preformed surface nanobubbles will be affected. This paper will thus readdress the long-held universal notion that added salt, no matter in what concentration, will not influence the properties of preformed surface nanobubble
Effect of impurities in the description of surface nanobubbles: Role of nonidealities in the surface layer\ud
In a recent study [ S. Das, J. H. Snoeijer and D. Lohse Phys. Rev. E 82 056310 (2010)], we provided quantitative demonstration of the conjecture [ W. A. Ducker Langmuir 25 8907 (2009)] that the presence of impurities at the surface layer (or the air-water interface) of surface nanobubbles can substantially lower the gas-side contact angle and the Laplace pressure of the nanobubbles. Through an analytical model for any general air-water interface without nonideality effects, we showed that a large concentration of soluble impurities at the air-water interface of the nanobubbles ensures significantly small contact angles (matching well with the experimental results) and Laplace pressure (though large enough to forbid stability). In this paper this general model is extended to incorporate the effect of nonidealities at the air-water interface in impurity-induced alteration of surface nanobubble properties. Such nonideality effects arise from finite enthalpy or entropy of mixing or finite ionic interactions of the impurity molecules at the nanobubble air-water interface and ensure significant lowering of the nanobubble contact angle and Laplace pressure even at relatively small impurity coverage. In fact for impurity molecules that show enhanced tendency to get adsorbed at the nanobubble air-water interface from the bulk phase, impurity-induced lowering of the nanobubble contact angle is witnessed for extremely small bulk concentration. Surface nanobubble experiments being typically performed in an ultraclean environment, the bulk concentration of impurities is inevitably very small, and in this light the present calculations can be viewed as a satisfactory explanation of the conjecture that impurities, even in trace concentration, have significant impact on surface nanobubble
Practically secure quantum position verification
We discuss quantum position verification (QPV) protocols in which the
verifiers create and send single-qubit states to the prover. QPV protocols
using single-qubit states are known to be insecure against adversaries that
share a small number of entangled qubits. We introduce QPV protocols that are
practically secure: they only require single-qubit states from each of the
verifiers, yet their security is broken if the adversaries share an
impractically large number of shared entangled qubits. These protocols are a
modification of known QPV protocols in which we include a classical random
oracle without altering the amount of quantum resources needed by the
verifiers. We present a cheating strategy that requires a number of entangled
qubits shared among the adversaries that grows exponentially with the size of
the classical input of the random oracle.Comment: v2: corrected errors, more detailed discussio
Steric-effect-induced enhancement of electrical-double-layer overlapping phenomena\ud
In this paper, we demonstrate that nontrivial interactions between steric effect and electrical-double-layer (EDL) overlap phenomena may augment the effective extent of EDL overlap in narrow fluidic confinements to a significant extent by virtue of rendering the channel centerline potential tending to the ζ potential in a limiting sense as the steric effect progressively intensifies. Such a behavior may result in a virtually uniform (undiminished) magnitude of the EDL potential across the entire channel height and may cause lowering of the total charge within the EDL.\ud
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Quantum reading capacity: General definition and bounds
Quantum reading refers to the task of reading out classical information
stored in a read-only memory device. In any such protocol, the transmitter and
receiver are in the same physical location, and the goal of such a protocol is
to use these devices (modeled by independent quantum channels), coupled with a
quantum strategy, to read out as much information as possible from a memory
device, such as a CD or DVD. As a consequence of the physical setup of quantum
reading, the most natural and general definition for quantum reading capacity
should allow for an adaptive operation after each call to the channel, and this
is how we define quantum reading capacity in this paper. We also establish
several bounds on quantum reading capacity, and we introduce an
environment-parametrized memory cell with associated environment states,
delivering second-order and strong converse bounds for its quantum reading
capacity. We calculate the quantum reading capacities for some exemplary memory
cells, including a thermal memory cell, a qudit erasure memory cell, and a
qudit depolarizing memory cell. We finally provide an explicit example to
illustrate the advantage of using an adaptive strategy in the context of
zero-error quantum reading capacity.Comment: v3: 17 pages, 2 figures, final version published in IEEE Transactions
on Information Theor
Quantum rebound capacity
Inspired by the power of abstraction in information theory, we consider
quantum rebound protocols as a way of providing a unifying perspective to deal
with several information-processing tasks related to and extending quantum
channel discrimination to the Shannon-theoretic regime. Such protocols, defined
in the most general quantum-physical way possible, have been considered in the
physical context of the DW model of quantum reading [Das and Wilde,
arXiv:1703.03706]. In [Das, arXiv:1901.05895], it was discussed how such
protocols apply in the different physical context of round-trip communication
from one party to another and back. The common point for all quantum rebound
tasks is that the decoder himself has access to both the input and output of a
randomly selected sequence of channels, and the goal is to determine a message
encoded into the channel sequence. As employed in the DW model of quantum
reading, the most general quantum-physical strategy that a decoder can employ
is an adaptive strategy, in which general quantum operations are executed
before and after each call to a channel in the sequence. We determine lower and
upper bounds on the quantum rebound capacities in various scenarios of
interest, and we also discuss cases in which adaptive schemes provide an
advantage over non-adaptive schemes in zero-error quantum rebound protocols.Comment: v2: published version, 7 pages, 2 figures, see companion paper at
arXiv:1703.0370
Bipartite Quantum Interactions: Entangling and Information Processing Abilities
The aim of this thesis is to advance the theory behind quantum information
processing tasks, by deriving fundamental limits on bipartite quantum
interactions and dynamics, which corresponds to an underlying Hamiltonian that
governs the physical transformation of a two-body open quantum system. The goal
is to determine entangling abilities of such arbitrary bipartite quantum
interactions. Doing so provides fundamental limitations on information
processing tasks, including entanglement distillation and secret key
generation, over a bipartite quantum network. We also discuss limitations on
the entropy change and its rate for dynamics of an open quantum system weakly
interacting with the bath. We introduce a measure of non-unitarity to
characterize the deviation of a doubly stochastic quantum process from a
noiseless evolution.
Next, we introduce information processing tasks for secure read-out of
digital information encoded in read-only memory devices against adversaries of
varying capabilities. The task of reading a memory device involves the
identification of an interaction process between probe system, which is in
known state, and the memory device. Essentially, the information is stored in
the choice of channels, which are noisy quantum processes in general and are
chosen from a publicly known set. Hence, it becomes pertinent to securely read
memory devices against scrutiny of an adversary. In particular, for a secure
read-out task called private reading when a reader is under surveillance of a
passive eavesdropper, we have determined upper bounds on its performance. We do
so by leveraging the fact that private reading of digital information stored in
a memory device can be understood as secret key agreement via a specific kind
of bipartite quantum interaction.Comment: PhD Thesis (minor revision). Also available at:
https://digitalcommons.lsu.edu/gradschool_dissertations/4717
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