# 2021

**Framework for resource quantification in infinite-dimensional general probabilistic theories**, L. Lami, B. Regula, R. Takagi, and G. Ferrari, Phys. Rev. A 103, 032424

DOI: doi.org/10.1103/PhysRevA.103.032424

#### The gist of it

It is well established that several features of quantum mechanical systems with no classical counterparts can be exploited as resources in practical applications, such as communication, computation, sensing and cryptography. It is then of paramount importance to rigorously quantify such an advantage, especially in relation to some explicit task that one might want to perform in a realistic scenario. In these two papers, we study the (generalized) robustness as a measure of a very large family of generic quantum resources, and its relation with a key task in quantum information: quantum channel discrimination. In particular, we prove that the robustness precisely quantifies the maximum advantage given by a resourceful state with respect to any free one, when used as a probe to determine which physical evolution it underwent. Our framework can be applied well beyond standard finite-dimensional quantum theory, and in particular, to all finite- and infinite-dimensional general probabilistic theories, i.e., generalizations of quantum mechanics itself. This is interesting both from a fundamental and practical perspective, as many resources needed for quantum technologies, e.g. nonclassicality and non-Gaussianity, are peculiar of systems with an associated infinite-dimensional Hilbert space.

**Operational Quantification of Continuous-Variable Quantum Resources**, B. Regula, L. Lami, G. Ferrari, and R. Takagi, Phys. Rev. Lett. 126, 110403,

DOI: doi.org/10.1103/PhysRevLett.126.110403

#### The gist of it

It is well established that several features of quantum mechanical systems with no classical counterparts can be exploited as resources in practical applications, such as communication, computation, sensing and cryptography. It is then of paramount importance to rigorously quantify such an advantage, especially in relation to some explicit task that one might want to perform in a realistic scenario. In these two papers, we study the (generalized) robustness as a measure of a very large family of generic quantum resources, and its relation with a key task in quantum information: quantum channel discrimination. In particular, we prove that the robustness precisely quantifies the maximum advantage given by a resourceful state with respect to any free one, when used as a probe to determine which physical evolution it underwent. Our framework can be applied well beyond standard finite-dimensional quantum theory, and in particular, to all finite- and infinite-dimensional general probabilistic theories, i.e., generalizations of quantum mechanics itself. This is interesting both from a fundamental and practical perspective, as many resources needed for quantum technologies, e.g. nonclassicality and non-Gaussianity, are peculiar of systems with an associated infinite-dimensional Hilbert space.

**Parallel selective nuclear-spin addressing for fast high-fidelity quantum gates**, B. Tratzmiller, J. F. Haase, Z. Wang, and M. B. Plenio, Phys. Rev. A 103, 012607

DOI: doi.org/10.1103/PhysRevA.103.012607

#### The gist of it

Due to their long coherence times, nuclear spins have gained considerable attention as physical qubits. Their interaction can be mediated by nitrogen vacancy (NV) centers in diamond. In this work we generalize PulsePol, a pulse sequence developed in the Institute of Theoretical Physics to achieve robust polarization transfer from NV centers to nuclear spins, to a sequence that is resonant to two frequencies simultaneously, allowing to perform gates between two nuclear spins.

This approach results in efficient entangling gates that, compared to standard techniques, reduce the gate time by more than 50% when the gate time is limited by off-resonant coupling to other spins, and by up to 22% when the gate time is limited by small electron-nuclear coupling.

**Precise Spectroscopy of High-Frequency Oscillating Fields with a Single-Qubit Sensor**, Y. Chu, P. Yang, M. Gong, M. Yu, B. Yu, M. B. Plenio, A. Retzker, and J. Cai, Phys. Rev. Applied 15, 014031

DOI: doi.org/10.1103/PhysRevApplied.15.014031

# News

Martin Plenio is listed as highly cited researcher for the fourth time in a row.

Our work on Quantum Physics and Biology featured Local and National Radio

Ludovico Lami wins a Humboldt Fellowship to continue his work in our group for another 2 years

Martin Plenio is selected as Highly Cited Researcher for 2019!

# Most Recent Papers

**Framework for resource quantification in infinite-dimensional general probabilistic theories**, Phys. Rev. A 103, 032424

**Operational Quantification of Continuous-Variable Quantum Resources**, Phys. Rev. Lett. 126, 110403

**Parallel selective nuclear-spin addressing for fast high-fidelity quantum gates**, Phys. Rev. A 103, 012607

# Contact

Ulm University

Institute of Theoretical Physics

Albert-Einstein-Allee 11

D - 89069 Ulm

Germany

Tel: ++49 / 731 / 50 - 22911

Fax: ++49 / 731 / 50 - 22924

Office: Building M26, room 4117

Click here if you are interested in applying to the group