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TZID:Europe/Madrid
BEGIN:STANDARD
DTSTART:20171029T030000
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
RDATE:20181028T030000,20191027T030000
TZNAME:CET
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BEGIN:DAYLIGHT
DTSTART:20180325T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
RDATE:20190331T020000
TZNAME:CEST
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BEGIN:VEVENT
UID:calendar.872.field_event_datetime.0@grupsderecerca.uab.cat/giq
DTSTAMP:20180522T021611Z
CREATED:20180427T104706Z
DESCRIPTION:I will present an investigation into thermodynamic cycles in ul
tra cold atoms when the interactions between the atoms plays in important
role. The first example uses a Bose–Einstein condensate with nonlinear in
teractions as the working medium and exploits a Feshbach resonance to chan
ge the interaction strength of the BEC. This allows to produce work by exp
anding and compressing the gas\, and the power-output can be optimised usi
ng a shortcut-to-adiabticity.\n\n\nThe second example investigates the ope
ration of a quantum Otto cycle near a quantum critical point. Specifically
we look at the pinning transition of a Tonks-Girardeau gas\, when particl
es will become pinned at the minima of an optical lattice if they are comm
ensurate with the number of lattice sites. Due to the energy gap opened at
the pinning transition this provides a performance boost to the many-body
system over a comparable ensemble of single particle engines.
DTSTART;TZID=Europe/Madrid:20180503T120000
DTEND;TZID=Europe/Madrid:20180503T120000
LAST-MODIFIED:20180427T104706Z
LOCATION:GIQ Seminar Room
SUMMARY:Efficient Quantum Engines in Interacting Ultracold Gases
URL;TYPE=URI:http://grupsderecerca.uab.cat/giq/node/872
END:VEVENT
BEGIN:VEVENT
UID:calendar.876.field_event_datetime.0@grupsderecerca.uab.cat/giq
DTSTAMP:20180522T021611Z
CREATED:20180507T102218Z
DESCRIPTION:Any two arbitrary quantum states\, acting on a given Hilbert sp
ace\, need not be related by a majorization ordering\, even if they are cl
ose to each other. Surprisingly\, however\, we prove that for any given st
ate\, and a ball of radius c around it (in trace distance) there exist two
states in the ball\, one which is majorized by all other states in it\, a
nd one which majorizes all other states in it. This result has diverse app
lications\, e.g.\, \n(i) in establishing continuity bounds for Schur conca
ve functions\, in particular for classes of entropies which arise naturall
y in quantum information theory\, \n(ii) in approximate LOCC conversions o
f pure bipartite states\, and \n(iii) in quantum state preparation. \nIn o
btaining the above result\, we first obtain a more general result which m
ight be of independent interest\, namely a necessary and sufficient condit
ion under which a state maximizes a concave and Gateaux-differentiable fun
ction in the ball. Examples of such a function include the von Neumann ent
ropy\, and the conditional entropy of bipartite states. Our proofs employ
tools from the theory of convex optimization under non-differentiable cons
traints\, in particular Fermat's Rule\, and majorization theory. This is j
oint work with Eric Hanson.
DTSTART;TZID=Europe/Madrid:20180510T140000
DTEND;TZID=Europe/Madrid:20180510T140000
LAST-MODIFIED:20180507T102218Z
LOCATION:Giq Seminar Room (C5/262)
SUMMARY:A surprising majorization relation and its applications
URL;TYPE=URI:http://grupsderecerca.uab.cat/giq/node/876
END:VEVENT
BEGIN:VEVENT
UID:calendar.877.field_event_datetime.0@grupsderecerca.uab.cat/giq
DTSTAMP:20180522T021611Z
CREATED:20180507T102751Z
DESCRIPTION:It has been a longstanding conjecture in entanglement theory th
at all PPT states in 3x3 dimensions have Schmidt number less than 2. Recen
tly\, this conjecture has been proven by Yang et al. Motivated by this res
ult we study Schmidt numbers of bipartite PPT states in higher dimensions.
We start by presenting an explicit construction of PPT states achieving S
chmidt numbers scaling linearly in the local dimension improving on previo
us constructions. Next\, we link the Schmidt number of a quantum state wri
tten as a block matrix to entangled sub-block matrices. We use this to sho
w that states invariant under partial transposition on the smaller of thei
r subsystems cannot have maximal Schmidt number. This generalizes a well-k
nown result by Kraus et al. Finally\, if time permits we discuss applicati
ons of these techniques to problems of channel compositions and most impor
tantly to the PPT squared conjecture. The first part of the talk is joint
with M. Huber\, L. Lami and C. Lancien\, and the second part with M. Chris
tandl and M. Wolf.
DTSTART;TZID=Europe/Madrid:20180510T170000
DTEND;TZID=Europe/Madrid:20180510T170000
LAST-MODIFIED:20180509T165407Z
LOCATION:GIQ Seminar Room (C5/262)
SUMMARY:Schmidt numbers of PPT states
URL;TYPE=URI:http://grupsderecerca.uab.cat/giq/node/877
END:VEVENT
BEGIN:VEVENT
UID:calendar.878.field_event_datetime.0@grupsderecerca.uab.cat/giq
DTSTAMP:20180522T021611Z
CREATED:20180507T103113Z
DESCRIPTION:We investigate sampling procedures that certify that an arbitra
ry \nquantum state on $n$ subsystems is close to an ideal mixed state \n$\
varphi^{\otimes n}$ for a given reference state $\varphi$\, up to \nerrors
on a few positions. This task makes no sense classically: it \nwould corr
espond to certifying that a given bitstring was generated \naccording to s
ome desired probability distribution. However\, in the \nquantum case\, th
is is possible if one has access to a prover who can \nsupply a purificati
on of the mixed state.\n\n\nIn this work\, we introduce the concept of mix
ed-state certification\, and \nwe show that a natural sampling protocol of
fers secure certification in \nthe presence of a possibly dishonest prover
: if the verifier accepts \nthen he can be almost certain that the state i
n question has been \ncorrectly prepared\, up to a small number of errors.
\n\n\nWe then apply this result to two-party quantum coin-tossing. Given t
hat \nstrong coin tossing is impossible\, it is natural to ask ``how close
can \nwe get'. This question has been well studied and is nowadays well
\nunderstood from the perspective of the bias of individual coin tosses.
\nWe approach and answer this question from a different---and somewhat \no
rthogonal---perspective\, where we do not look at individual coin tosses
\nbut at the global entropy instead. We show how two distrusting parties
\ncan produce a common high-entropy source\, where the entropy is an \narb
itrarily small fraction below the maximum (except with negligible \nprobab
ility).
DTSTART;TZID=Europe/Madrid:20180511T140000
DTEND;TZID=Europe/Madrid:20180511T140000
LAST-MODIFIED:20180507T103113Z
LOCATION:GIQ Seminar Room (C5/262)
SUMMARY:Sampling mixed quantum states
URL;TYPE=URI:http://grupsderecerca.uab.cat/giq/node/878
END:VEVENT
BEGIN:VEVENT
UID:calendar.874.field_event_datetime.0@grupsderecerca.uab.cat/giq
DTSTAMP:20180522T021611Z
CREATED:20180504T100304Z
DESCRIPTION:Resource theories in quantum information science are helpful fo
r the study and quantification of the performance of information-processin
g tasks that involve quantum systems. These resource theories also find ap
plications in the study of other areas\; e.g.\, the resource theories of e
ntanglement and coherence have found use and implications in the study of
quantum thermodynamics and memory effects in quantum dynamics. In this pap
er\, we introduce the resource theory of unextendibility\, which is associ
ated to the inability of extending quantum entanglement in a given quantum
state to multiple parties. The free states in this resource theory are th
e k-extendible states\, and the free channels are k-extendible channels\,
which preserve the class of k-extendible states. We make use of this resou
rce theory to derive non-asymptotic\, upper bounds on the rate at which qu
antum communication or entanglement preservation is possible by utilizing
an arbitrary quantum channel a finite number of times\, along with the ass
istance of k-extendible channels at no cost. We then show that the bounds
we obtain are significantly tighter than previously known bounds for both
the depolarizing and erasure channels.
DTSTART;TZID=Europe/Madrid:20180515T120000
DTEND;TZID=Europe/Madrid:20180515T120000
LAST-MODIFIED:20180508T150221Z
LOCATION:GIQ Seminar Room (C5/262)
SUMMARY:Extendibility limits the performance of quantum processors
URL;TYPE=URI:http://grupsderecerca.uab.cat/giq/node/874
END:VEVENT
BEGIN:VEVENT
UID:calendar.879.field_event_datetime.0@grupsderecerca.uab.cat/giq
DTSTAMP:20180522T021611Z
CREATED:20180509T165835Z
DESCRIPTION:We develop a general framework characterizing the structure and
properties of quantum resource theories for continuous-variable Gaussian
states and Gaussian operations\, establishing methods for their descriptio
n and quantification. We show in particular that\, under a few intuitive a
nd physically-motivated assumptions on the set of free states\, no Gaussia
n quantum resource can be distilled with Gaussian free operations\, even w
hen an unlimited supply of the resource state is available. This places fu
ndamental constraints on state transformations in all such Gaussian resour
ce theories. Our methods rely on the definition of a general Gaussian reso
urce quantifier whose value does not change when multiple copies are consi
dered. We discuss in particular the applications to quantum entanglement\,
where we extend previously known results by showing that Gaussian entangl
ement cannot be distilled even with Gaussian operations preserving the pos
itivity of the partial transpose\, as well as to other Gaussian resources
such as steering and optical non classicality.
DTSTART;TZID=Europe/Madrid:20180515T150000
DTEND;TZID=Europe/Madrid:20180515T150000
LAST-MODIFIED:20180509T165835Z
LOCATION:GIQ Seminar Room (C5/262)
SUMMARY:Gaussian quantum resource theories
URL;TYPE=URI:http://grupsderecerca.uab.cat/giq/node/879
END:VEVENT
BEGIN:VEVENT
UID:calendar.882.field_event_datetime.0@grupsderecerca.uab.cat/giq
DTSTAMP:20180522T021611Z
CREATED:20180514T084632Z
DESCRIPTION:We investigate monogamy of correlations in the Bloch representa
tion. Here\, monogamy of correlations can be understood as direct relation
s between different correlation tensor elements. \nTo that end we introduc
e the split Bloch basis\, that is particularly useful for representing qua
ntum states with low dimensional support and thus amenable to purification
arguments.
DTSTART;TZID=Europe/Madrid:20180517T120000
DTEND;TZID=Europe/Madrid:20180517T120000
LAST-MODIFIED:20180514T084632Z
LOCATION:GIQ Seminar Room
SUMMARY:Monogamy of correlations in the Bloch picture
URL;TYPE=URI:http://grupsderecerca.uab.cat/giq/node/882
END:VEVENT
BEGIN:VEVENT
UID:calendar.875.field_event_datetime.0@grupsderecerca.uab.cat/giq
DTSTAMP:20180522T021611Z
CREATED:20180507T101517Z
DESCRIPTION:Photonic states with large and fixed photon numbers\, such as F
ock states\, enable quantum-enhanced metrology but remain an experimentall
y elusive resource. A potentially simple\, deterministic and scalable way
to generate these states consists of fully exciting N quantum emitters equ
ally coupled to a common photonic reservoir\, which leads to a collective
decay known as Dicke superradiance. The emitted N-photon state turns out t
o be a highly entangled multimode state\, and to characterise its metrolog
ical properties in this work we: (i) develop theoretical tools to compute
the Quantum Fisher Information of general multimode photonic states\; (ii)
use it to show that Dicke superradiant photons in 1D waveguides achieve H
eisenberg scaling\, which can be saturated by a parity measurement\; (iii)
and study the robustness of these states to experimental limitations in s
tate-of-art atom-waveguide QED setups.\n\n\n
DTSTART;TZID=Europe/Madrid:20180530T120000
DTEND;TZID=Europe/Madrid:20180530T120000
LAST-MODIFIED:20180507T101517Z
LOCATION:GIQ Seminar Room (C5/262)
SUMMARY:Quantum metrology with one-dimensional superradiant photonic states
URL;TYPE=URI:http://grupsderecerca.uab.cat/giq/node/875
END:VEVENT
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