1,190 research outputs found
Entanglement between two superconducting qubits via interaction with non-classical radiation
We propose a scheme to physically interface superconducting nano-circuits and
quantum optics. We address the transfer of quantum information between systems
having different physical natures and defined in Hilbert spaces of different
dimensions. In particular, we investigate the transfer of the entanglement
initially in a non-classical state of a continuous-variable system to a pair of
superconducting charge qubits. This set-up is able to drive an initially
separable state of the qubits into an almost pure, highly entangled state
suitable for quantum information processing.Comment: 4 pages, RevTeX; revised versio
Information transmission over an amplitude damping channel with an arbitrary degree of memory
We study the performance of a partially correlated amplitude damping channel
acting on two qubits. We derive lower bounds for the single-shot classical
capacity by studying two kinds of quantum ensembles, one which allows to
maximize the Holevo quantity for the memoryless channel and the other allowing
the same task but for the full-memory channel. In these two cases, we also show
the amount of entanglement which is involved in achieving the maximum of the
Holevo quantity. For the single-shot quantum capacity we discuss both a lower
and an upper bound, achieving a good estimate for high values of the channel
transmissivity. We finally compute the entanglement-assisted classical channel
capacity.Comment: 17 pages, 7 figure
Characterization of coherent impurity effects in solid state qubits
We propose a characterisation of the effects of bistable coherent impurities
in solid state qubits. We introduce an effective impurity description in terms
of a tunable spin-boson environment and solve the dynamics for the qubit
coherences. The dominant rate characterizing the asymptotic time limit is
identified and signatures of non-Gaussian behavior of the quantum impurity at
intermediate times are pointed out. An alternative perspective considering the
qubit as a measurement device for the spin-boson impurity is proposed.Comment: 4 pages, 5 figures. Replaced with published version, minor change
Correlated tunneling into a superconductor in a multiprobe hybrid structure
We consider tunneling in a hybrid system consisting of a superconductor with
two or more probe electrodes which can be either normal metals or polarized
ferromagnets. In particular we study transport at subgap voltages and
temperatures. Besides Andreev pair tunneling at each contact, in multi-probe
structures subgap transport involves additional channels, which are due to
coherent propagation of two particles (electrons or holes), each originating
from a different probe electrode. The relevant processes are electron
cotunneling through the superconductor and conversion of two electrons stemming
from different probes in a Cooper pair. These processes are non-local and decay
when the distance between the pair of involved contacts is larger than the
superconducting coherence length. The conductance matrix of a the three
terminal hybrid structure is calculated. The multi-probe processes enhance the
conductance of each contact. If the contacts are magnetically polarized the
contribution of the various conduction channels may be separately detected.Comment: 7 pages, 1 figure, accepted in Europhysics Letters, minor changes, 3
references adde
Decoherence due to telegraph and 1/f noise in Josephson qubits
We study decoherence due to random telegraph and 1/f noise in Josephson
qubits. We illustrate differences between gaussian and non gaussian effects at
different working points and for different protocols. Features of the
intrinsically non-gaussian and non-Markovian low-frequency noise may explain
the rich physics observed in the spectroscopy and the dynamics of charge based
devices.Comment: 6 pages, 4 figures. Proceedings of the International Symposium on
Mesoscopic Superconductivity and Spintronics 2004 (MS+S2004), Atsugi, Japa
Classical and quantum capacities of a fully correlated amplitude damping channel
We study information transmission over a fully correlated amplitude damping
channel acting on two qubits. We derive the single-shot classical channel
capacity and show that entanglement is needed to achieve the channel best
performance. We discuss the degradability properties of the channel and
evaluate the quantum capacity for any value of the noise parameter. We finally
compute the entanglement-assisted classical channel capacity.Comment: 16 pages, 9 figure
Cracking Down on Cutting Sleeves: A Historical Analysis of “Homosexuality” in China as a Comparison to Present Day LGBTQ+ Rights
Over the past more than a decade of Xi Jinping’s leadership, the space for civil society in China has shrunk dramatically. One of the main, yet often overlooked, victims of this shift in policy has been China’s LGBTQ+ community. This thesis examines the current crackdown on LGBTQ+ peoples and organizations in China and attempts to place it within a broader context of China’s current state in the world order. The lenses of queer International Relations theory and the long history of “homosexuality” in China will both be applied to help contextualize the current state of Chinese LGBTQ+ rights. This analysis will also present a comprehensive timeline of the various events and actions taken by the current Chinese state to suppress this community to demonstrate the systemic level nature of this crackdown. Drawing on these two frameworks, this thesis argues that the political deployment of homophobia and associated suppression of LBGTQ+ rights in China is used to consolidate identities, enforce heteronormative forms of behavior, and ultimately to consolidate the power, legitimacy, and control of Xi Jinping and the Communist Party of China
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