411,756 research outputs found
Quantum cloning
The impossibility of perfectly copying (or cloning) an arbitrary quantum
state is one of the basic rules governing the physics of quantum systems. The
processes that perform the optimal approximate cloning have been found in many
cases. These "quantum cloning machines" are important tools for studying a wide
variety of tasks, e.g. state estimation and eavesdropping on quantum
cryptography. This paper provides a comprehensive review of quantum cloning
machines (both for discrete-dimensional and for continuous-variable quantum
systems); in addition, it presents the role of cloning in quantum cryptography,
the link between optimal cloning and light amplification via stimulated
emission, and the experimental demonstrations of optimal quantum cloning
Special Libraries, March 1955
Volume 46, Issue 3https://scholarworks.sjsu.edu/sla_sl_1955/1002/thumbnail.jp
Quantum deleting and Signalling
It is known that if we can clone an arbitrary state we can send signal faster
than light. Here, we show that deletion of unknown quantum state against a copy
can lead to superluminal signalling. But erasure of unknown quantum state does
not imply faster than light signalling.Comment: Latex file, 6 pages, no figure
Campus Update: May 1994 v. 6, no. 4
Monthly newsletter of the BU Medical Campu
A Template for Implementing Fast Lock-free Trees Using HTM
Algorithms that use hardware transactional memory (HTM) must provide a
software-only fallback path to guarantee progress. The design of the fallback
path can have a profound impact on performance. If the fallback path is allowed
to run concurrently with hardware transactions, then hardware transactions must
be instrumented, adding significant overhead. Otherwise, hardware transactions
must wait for any processes on the fallback path, causing concurrency
bottlenecks, or move to the fallback path. We introduce an approach that
combines the best of both worlds. The key idea is to use three execution paths:
an HTM fast path, an HTM middle path, and a software fallback path, such that
the middle path can run concurrently with each of the other two. The fast path
and fallback path do not run concurrently, so the fast path incurs no
instrumentation overhead. Furthermore, fast path transactions can move to the
middle path instead of waiting or moving to the software path. We demonstrate
our approach by producing an accelerated version of the tree update template of
Brown et al., which can be used to implement fast lock-free data structures
based on down-trees. We used the accelerated template to implement two
lock-free trees: a binary search tree (BST), and an (a,b)-tree (a
generalization of a B-tree). Experiments show that, with 72 concurrent
processes, our accelerated (a,b)-tree performs between 4.0x and 4.2x as many
operations per second as an implementation obtained using the original tree
update template
Digital controller for a Baum folding machine
A digital controller for controlling the operation of a folding machine enables automatic folding of a desired number of sheets responsive to entry of that number into a selector. The controller includes three decade counter stages for corresponding rows of units, tens and hundreds push buttons. Each stage including a decimal-to-BCD encoder, a buffer register, and a digital or binary counter. The BCD representation of the selected count for each digit is loaded into the respective decade down counters. Pulses generated by a sensor and associated circuitry are used to decrease the count in the decade counters. When the content of the decade counter reaches either 0 or 1, a solenoid control valve is actuated which interrupts operation of the machine. A repeat switch, when actuated, prevents clearing of the buffer registers so that multiple groups of the same number of sheets can be folded without reentering the number into the selector
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