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Düsseldorf Quantum Info Online Seminars

Friday, April 16, 10:30
Location: ZOOM https://us02web.zoom.us/j/82770347404
Speaker: Roberto Ferrara, Technical University of Munich, Germany

Friday, April 30, 10:30
Location: ZOOM https://us02web.zoom.us/j/82770347404
Speaker: Mirjam Weilenmann, IQOQI Vienna, Austria
Quantum Physics Needs Complex Numbers

Friday, May 14, 10:30
Location: ZOOM https://us02web.zoom.us/j/82770347404
Speaker: Daniel Stilck França, University of Copenhagen, Denmark

Title: A game of quantum advantage: linking verification and simulation

Abstract: We present a formalism that captures the process of proving quantum
superiority to skeptics as an interactive game between two agents, supervised by
a referee. Bob, is sampling from a classical distribution on a quantum device
that is supposed to demonstrate a quantum advantage. The other player, the
skeptical Alice, is then allowed to propose mock distributions supposed to
reproduce Bob's device's statistics. He then needs to provide witness functions
to prove that Alice's proposed mock distributions cannot properly approximate
his device. Within this framework, we establish three results. First, for random
quantum circuits, Bob being able to efficiently distinguish his distribution
from Alice's implies efficient approximate simulation of the distribution.
Secondly, finding a polynomial time function to distinguish the output of random
circuits from the uniform distribution can also spoof the heavy output
generation problem in polynomial time. This pinpoints that exponential resources
may be unavoidable for even the most basic verification tasks in the setting of
random quantum circuits.

Beyond this setting, by employing strong data processing inequalities, our
framework allows us to analyse the effect of noise on classical simulability and
verification of more general near-term quantum advantage proposals.

Friday, May 21, 10:30
Location: Webex https://hhu.webex.com/join/glaucia_murta
Speaker: David Edward Bruschi, Forschungszentrum Jülich, Germany

Title: Quantum communication with satellites in curved spacetime

Abstract: Quantum communication aims at sharing secure information, that is
protected from malicious attacks by the laws of physics, between interested
parties. In recent years, space-based satellite links that exchange photons
through empty space have been viewed as good candidates to build a quantum
communication network. This approach overcomes the fundamental distance
limitations inherent to fibre-based networks, potentially extending the network
to arbitrary distances, and guarantees secure communications around the globe
that would be difficult to physically attack. The Chinese Academy of Sciences
has recently launched the first dedicated satellite for quantum communication,
that will be used for a myriad of different applications. Regardless of the fact
that gravity is unavoidable when considering moving any technological platform
to space, the effects of gravity on quantum communication protocols have so far
been ignored.
I have recently closed this gap by using tools from quantum field theory in
(weakly) curved spacetime to correctly incorporate the effects of the Earth’s
spacetime curvature on photon propagation between a source and a satellite. I
will discuss my results, which show that: (i) quantum communication can be less
secure if gravitational effects on propagating photons are not considered; (ii)
gravitational effects on the frequency distribution or polarisation of
propagating photons can be used to measure precisely distances and the mass of
the Earth; (iii) the effects of the rotation of our planet can also be included.
Future work and outlook will also be discussed.

Friday, June 11, 10:30
Location: ZOOM https://us02web.zoom.us/j/82770347404
Speaker: Timo Simnacher, Universität Siegen, Germany


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