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CATEGORIES:Cold Atoms
SUMMARY:Computation and metrology with cold atoms in mixed
states - Silvia Bergamini (Open University)
DTSTART:20151016T130000Z
DTEND:20151016T140000Z
UID:TALK1806AT
URL:/talk/index/1806
DESCRIPTION:The use of Rydberg interactions and ensembles of c
old atoms in mixed state for the implementation\no
f a protocol for deterministic quantum computation
with one quantum bit (DQC1 [1]) is discussed.\nTh
is protocol relies on one pure control qubit toget
her with a register of completely-mixed qubits.\nD
QC1 is a non-universal model that can speed up som
e computational tasks for which no efficient\nclas
sical algorithms are known. Whilst requiring only
a single qubit with coherence\, for these specific
\ntasks\, its power scales up with the number of q
ubits in a mixed state. Although it has been\nshow
n that this scheme contains little to no entanglem
ent\, non-classical correlations are present in\nt
he output state of the DQC1 which can be quantifie
d in terms of quantum discord. To date\, successfu
l\nexperiments based on DQC1 have evaluated the no
rmalised trace of a two-by-two unitary\nmatrix [2]
and performed the approximation to the Jones poly
nomial with a system of four qubits\,\nthus demons
trating the ground principle of mixed state comput
ation.\nWe propose an experimental test for the tr
ue scalability of the protocol based on cold atoms
and Ryderg interactions\nand to study the physics
of discord\, as well as the strategy for extendin
g to non-trivial problems [3]\, such as many-body
physics.\nA scheme is also presented for quantum p
hase estimation. This is derived from the DQC1 mo
del and promises to enable quantum enhanced\nmeasu
rement\, without relying on quantum entanglement a
nd only using discord in the probe states [4].\nMo
delling of this scheme\, using cold atoms in dipol
e traps\, demonstrates\nthat the register of partl
y mixed qubits becomes a powerful resource for pha
se estimation\nwhen supplied with the coherence fr
om the control qubit.\n\nReferences\n[1] Knill E a
nd Laflamme R 1998 Power of one bit of quantum inf
ormation Phys. Rev. Lett. 81\,\n5672 (1998)\n\n[2]
Lanyon B P\, Barbieri M\, Almeida M P and White A
G 2008 Experimental quantum computing\nwithout en
tanglement Phys. Rev. Lett. 101 200501 (2008)\n\n[
3] C W Mansell\, S Bergamini A cold-atoms based pr
ocessor for deterministic quantum computation\nwit
h one qubit in intractably large Hilbert spaces Ne
w J. Phys. 16 053045 (2014)\n\n[4] Modi K\, Cable
H\, Williamson M and Vedral V 2011 Quantum correla
tions
LOCATION:Physics East 217
CONTACT:Vincent Boyer
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