3. Physikalisches Institut

Open positions

Opportunity to participate and contribute to research on applicative quantum science

Master/Bachelor Thesis

Modern quantum information processing relies on fast and precise control of quantum bits. Algorithms require the fidelity of each operation to exceed 99% and indeed scalable quantum computers require even larger numbers. Achieving such high precision requires sophisticated quantum control. In the thesis we will apply quantum optimal control algorithms to single quantum bits. This numerical method achieves high gate fidelities by optimizing quantum control under a predefined stet of boundary conditions. We will install these algorithms on new ultrafast hardware with the goal to attain increased precision in quantum error correction. The achieved gain in fidelity will be experimentally tested and the developed software will be integrated into an existing software package.

Contact: Prof. Dr. Jörg Wrachtrup

Over the past years, we assembled a cryogenic “quantum microscope” which employs an optically interrogated electronic spin qubit consisting of a nitrogen vacancy center located roughly 10nm below the surface of a diamond probe. Scanning this sensor across the surface of a specimen allows for the detection and imaging of extremely weak magnetic fields with nanometer spatial resolution.

Given the ability of the microscope to measure over a wide range of temperatures and external magnetic fields, we plan to map the phase space of skyrmion host materials, such as Cu2OSeO3 showing skyrmionic, helical, para- and ferromagnetic phases [1]. In the skyrmionic phase, we will study the dynamics of skyrmions, namely eigenmodes, or resonant modes, covering the three established excitation types anticlockwise and clockwise gyration modes and breathing modes.

This work covers a unique combination of many technical skills like confocal microscopy, microwave resonator engineering, tuning-fork AFM techniques, cryogenics, cleanroom sample preparation and single-photon counting signal processing with a variety of solid-state measurement techniques like ODMR, T1/T2 relaxometry and spin-noise spectroscopy to finally gain deep insight into the physics that determines the spin structures of the different phases.

[1] Science 336 (6078), 198-201

Contact: Dr. Rainer Stöhr

Hybrid quantum devices, which combine solid-state spins with macroscopic mechanical oscillators, are currently of great interest with the aim to explore the quantum regime of macroscopic mechanical objects.

We are currently working on the coupling between phonons and single electron spins associated with NV centers in diamond. The coupling is given by either strain-mediated coupling or magnetic field gradient coupling and the macroscopic oscillators can either be optically actuated or mechanically excited.

We want to develop new clever hybrid device geometries with increased spin-phonon coupling with the intention to detect radiation pressure, develop a sensor for high sensitivity mass detection or, in general, explore new sensor modalities such as exceptional point sensors.

This works touches many aspects of micro-/nanomechanical device fabrication using standard cleanroom techniques such as electron beam lithography, plasma etching and ion implantation while as the same time requires different measurement techniques to detect the motion of the mechanical system but also to measure the influence of the motion on the coherence properties of the spin qubit associated with the NV center.

Contact: Dr. Rainer Stöhr


Recently, tetragonal Heusler materials have been discovered to host magnetic antiskyrmions even above room temperature, which is a groundbreaking step towards their applications in spintronics [1].

Using our room temperature confocal scanning probe setup, we are able to scan a single NV center over the surface of a sample at a vertical distance of about 10nm. This allows for quantitative measures of the magnitude and direction of the magnetic fields associated with the antiskyrmion lattice at nanometer spatial resolution.

First, we want to image the skyrmion lattice and determine its basic properties such as lateral dimensions or strength and direction of magnetic field. Then, we want to study the influence of external stimuli like AC electric or magnetic fields on the temporal evolution of individual skyrmions but also on the entire lattice.

This work covers a range of experimental techniques like confocal microscopy, microwave resonator engineering and tuning-fork AFM techniques. At the same time, it requires a profound knowledge of the sensing capabilities of the NV center spin qubit as well as a deep understanding of the physics governing the Heusler material.

 [1] Nature volume548, pages561–566 (31 August 2017)

Contact: Dr. Rainer Stöhr

The aim would be to demonstrate the minimal model of a quantum heat machine (for both quantum heat engines and refrigerators) made of a single driven two-level NV qubit simultaneously coupled to spectrally distinct hot and cold baths. The dependence of the quantum refrigerator cooling rate and efficiency on the bath spectra and modulation rate of the coupling between the qubit and the baths will be analysed both theoretically and experimentally. For experiments two spin-baths made of 13C nuclear spins will be used to demonstrate the working principle of the Quantum Refrigerator.

Contact: Dr. Durga Dasari

The aim here would be to use quantum control theory to design methods to sense the dynamics of strongly interacting many-spin systems, which include 2D spin models, Skyrmions, spin-Maser etc. Using both analytical and computational methods, you will produce a library of pulse sequences with targeted functionality in sensing interacting spin systems. Further, (as time permits) you will use these results to design a sequence for detecting thermalization in closed systems using a quantum sensor.

Contact: Dr. Durga Dasari


Rare earth ions in optical crystals are potentially excellent candidates for quantum computing applications as qubits and quantum memory. So far, most of quantum features of rare earth ions were studied and exploited in ensembles containing many (billions) of ions. However, for scalable quantum computing single ion qubits are preferred. As of now, only two rare earth species, namely, cerium and praseodymium, were detected optically at a single ion level. Extending the list of detectable ions would strengthen the whole field of rare earth quantum computing.

The proposed master project is aiming at optical detection of a single divalent europium ion in various hosts. While some of the host materials, such as CaF2, are readily available as single crystals, the most interesting having no intrinsic nuclear spins ones can be obtained primarily as micro- and nano-powders. If the detection of Eu2+ ion is achieved at early stage of the project, the focus of the work will be shifted on studying electron and nuclear spin properties of the potential europium qubit.

The project will involve many aspects of materials science and optical characterization in confocal microscopes. It also implies close collaboration with material science groups at Max-Planck Institute as well as with implantation groups in Bochum, Augsburg, and Leipzig.

Interested applicants can contact Prof. Dr. Jörg Wrachtrup or Dr. Roman Kolesov by e-mails

Motivated students who are interested to join the Volkmer Lab in order to conduct scientific research for their thesis project are strongly encouraged to apply. Applicants should have a basic knowledge of ultrafast laser physics, nonlinear spectroscopy or quantum optics. A vital interest in macromolecular Biophysics is very helpful.
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Dr. A. Volkmer


Jörg Wrachtrup
Prof. Dr.

Jörg Wrachtrup

Head of Department

[Photo: David Ausserhofer]

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