2021

Coherence of operations and interferometry, M. Masini, T. Theurer, and M. B. Plenio, Phys. Rev. A 103, 042426
DOI: doi.org/10.1103/PhysRevA.103.042426

Picture of the Publication

Ground-State Cooling of Levitated Magnets in Low-Frequency Traps, K. Streltsov, J. S. Pedernales, and M. B. Plenio, Phys. Rev. Lett. 126, 193602
DOI: doi.org/10.1103/PhysRevLett.126.193602

The gist of it

The ability to operate massive particles in the quantum regime is predicted to bring exceptional enhancements in sensitivity for metrological applications, and enable fundamental tests of the nature of the gravitational interaction. Such control can be reached via cooling the particles to their quantum mechanical ground state. With increasing mass this turns into a progressively harder task. In this work we present a feedback cooling scheme that is capable of reaching the ground state of trapped magnetic particles with radii in the range of 1-10um.

Picture from the Publication

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.

Picture from the Publication

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.

Picture of the Publication

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.

 

Picture of the Publication

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

The gist of it

In recent years our group has been interested in the application of NV centers for the detection of weak classical or quasi-classical fields. In our earlier works (e.g. Schmitt et al, Science 2017) we had been interested in the detection of fields due to the precession of nuclear spins in an external magnetic field which finds application in NMR. Such fields oscillate in the MHz regime, but there is also considerable interest in the detection of fields in the GHz regime, that is microwaves. To achieve this, the pulsed schemes of our earlier works are hard to realise at sufficient rates so that we had to change the detection protocol employing continuous control fields, much in the spirit of optical heterodyne detection, that enable the comparison of the known driving field with the unknown high frequency signal field.

 

Most Recent Papers

Coherence of operations and interferometry, Phys. Rev. A 103, 042426

Ground-State Cooling of Levitated Magnets in Low-Frequency Traps, Phys. Rev. Lett. 126, 193602

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

 

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