ELFT HÍRADÓ

[Janos Asboth <asboth.janos AT ttk.bme.hu>]

Meghívó

BME Elméleti Fizika Szeminárium,

nov. 7. péntek 10h15,

1111 Budapest, Budafoki út 8., BME F III. magasföldszint 01.,
Elméleti Fizika Tanszék szemináriumi szoba

Fabian Ballar (Uni Augsburg):
Noise, Magic, and Error-Resilience in Encoding–Decoding Quantum Circuits

Nonstabilizerness, or magic, is a key quantum resource required for quantum
computational advantage. Noise is typically viewed as purely detrimental
because it drives quantum states toward classicality. However, the behavior
of magic under realistic noisy dynamics remains poorly understood, in part
due to the complexity of analyzing mixed-state magic.

In this talk, I will show that non-unital noise, exemplified by amplitude
damping, can preserve and even inject magic into quantum states. Building
on this observation, we present a proof-of-principle protocol that distills
pure magic states using access to the noisy channel alone.

We then investigate the behavior of encoding–decoding quantum circuits
under realistic noise models. Recent works suggest the presence of two
distinct transitions. One transition separates a phase that is
error-resilient, where the encoded logical state can be recovered, from a
phase where recovery fails. The other transition was found to occur in the
nonstabilizerness of the output states. We show that these two transitions
do not coincide in general. In particular, while an error-resilience
transition persists under realistic noise, we do not observe any transition
in magic.

Finally, we discuss what features of a unitary ensemble allow it to sustain
an error-resilient phase, shedding light on what makes a unitary "good" for
protecting quantum information in the presence of noise.

Minden érdeklődőt szeretettel várunk.
Asbóth János,
 szemináriumi koordinátor