1,581 research outputs found
Bidirectional coherent classical communication
A unitary interaction coupling two parties enables quantum communication in
both the forward and backward directions.
Each communication capacity can be thought of as a tradeoff between the
achievable rates of specific types of forward and backward communication.
Our first result shows that for any bipartite unitary gate, coherent
classical communication is no more difficult than classical communication --
they have the same achievable rate regions. Previously this result was known
only for the unidirectional capacities (i.e., the boundaries of the tradeoff).
We then relate the tradeoff curve for two-way coherent communication to the
tradeoff for two-way quantum communication and the tradeoff for coherent
communiation in one direction and quantum communication in the other.Comment: 11 pages, v2 extensive modification and rewriting of the main proof,
v3 published version with only a few more change
An exact effective two-qubit gate in a chain of three spins
We show that an effective two-qubit gate can be obtained from the free
evolution of three spins in a chain with nearest neighbor XY coupling, without
local manipulations. This gate acts on the two remote spins and leaves the
mediating spin unchanged. It can be used to perfectly transfer an arbitrary
quantum state from the first spin to the last spin or to simultaneously
communicate one classical bit in each direction. One ebit can be generated in
half of the time for state transfer.
For longer spin chains, we present methods to create or transfer entanglement
between the two end spins in half of the time required for quantum state
transfer, given tunable coupling strength and local magnetic field. We also
examine imperfect state transfer through a homogeneous XY chain.Comment: RevTeX4, 7 pages, 4 figue
Reversible simulation of bipartite product Hamiltonians
Consider two quantum systems A and B interacting according to a product
Hamiltonian H = H_A x H_B. We show that any two such Hamiltonians can be used
to simulate each other reversibly (i.e., without efficiency losses) with the
help of local unitary operations and local ancillas. Accordingly, all non-local
features of a product Hamiltonian -- including the rate at which it can be used
to produce entanglement, transmit classical or quantum information, or simulate
other Hamiltonians -- depend only upon a single parameter. We identify this
parameter and use it to obtain an explicit expression for the entanglement
capacity of all product Hamiltonians. Finally, we show how the notion of
simulation leads to a natural formulation of measures of the strength of a
nonlocal Hamiltonian.Comment: 10 page
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Examining the Relationships Among Categorization, Stereotype Activation, and Stereotype Application.
Increased category salience is associated with increased stereotyping. Prior research has not examined the processes that may account for this relationship. That is, it is unclear whether category salience leads to increased stereotyping by increasing stereotype activation (i.e., increased accessibility of stereotypic information), application (i.e., increasing the tendency to apply activated stereotypes), or both processes simultaneously. We examined this question across three studies by manipulating category salience in an implicit stereotyping measure and by applying a process model that provides independent estimates of stereotype activation and application. Our results replicated past findings that category salience increases stereotyping. Modeling results showed that category salience consistently increased the extent of stereotype application but increased stereotype activation in more limited contexts. Implications for models of social categorization and stereotyping are discussed
Quantum Data Hiding
We expand on our work on Quantum Data Hiding -- hiding classical data among
parties who are restricted to performing only local quantum operations and
classical communication (LOCC). We review our scheme that hides one bit between
two parties using Bell states, and we derive upper and lower bounds on the
secrecy of the hiding scheme. We provide an explicit bound showing that
multiple bits can be hidden bitwise with our scheme. We give a preparation of
the hiding states as an efficient quantum computation that uses at most one
ebit of entanglement. A candidate data hiding scheme that does not use
entanglement is presented. We show how our scheme for quantum data hiding can
be used in a conditionally secure quantum bit commitment scheme.Comment: 19 pages, IEEE style, 8 figures, submitted to IEEE Transactions on
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