69,082 research outputs found
Qubit-qudit states with positive partial transpose
We show that the length of a qubit-qutrit separable state is equal to the
max(r,s), where r is the rank of the state and s is the rank of its partial
transpose. We refer to the ordered pair (r,s) as the birank of this state. We
also construct examples of qubit-qutrit separable states of any feasible birank
(r,s). We determine the closure of the set of normalized two-qutrit entangled
states of rank four having positive partial transpose (PPT). The boundary of
this set consists of all separable states of length at most four. We prove that
the length of any qubit-qudit separable state of birank (d+1,d+1) is d+1. We
also show that all qubit-qudit PPT entangled states of birank (d+1,d+1) can be
built in a simple way from edge states. If V is a subspace of dimension k<d in
the tensor product of C^2 and C^d such that V contains no product vectors, we
show that the set of all product vectors in the orthogonal complement of V is a
vector bundle of rank d-k over the projective line. Finally, we explicitly
construct examples of qubit-qudit PPT states (both separable and entangled) of
any feasible birank.Comment: 13 pages, 2 table
Fluctuation-induced tunneling conduction through RuO nanowire contacts
A good understanding of the electronic conduction processes through
nanocontacts is a crucial step for the implementation of functional
nanoelectronic devices. We have studied the current-voltage (-)
characteristics of nanocontacts between single metallic RuO nanowires (NWs)
and contacting Au electrodes which were pre-patterned by simple
photolithography. Both the temperature behavior of contact resistance in the
low-bias voltage ohmic regime and the - curves in the high-bias voltage
non-ohmic regime have been investigated. We found that the electronic
conduction processes in the wide temperature interval 1--300 K can be well
described by the fluctuation-induced tunneling (FIT) conduction theory. Taken
together with our previous work (Lin {\it et al.}, Nanotechnology {\bf 19},
365201 (2008)) where the nanocontacts were fabricated by delicate electron-beam
lithography, our study demonstrates the general validity of the FIT model in
characterizing electronic nanocontacts.Comment: 6 pages, 5 figure
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