Research

We work at the interface of quantum information theory and experiments on quantum hardware. We try to devise concrete experimental protocols to put abstract theoretical ideas into practice. At the same time, we also explore specific experimental setups in order to identify challenges and opportunities for novel quantum information processing protocols. We have a particular interest in quantum sensing applications and quantum many-body dynamics.    

Recent projects

Realizing Bilayer Crystals of Trapped Ions

Trapped ions are a leading platform for quantum information processing, but they are currently limited to 1D chains or 2D planar crystals. In this project, we showed how Penning traps can be used to prepare clean two layered crystals of hundreds of ions, that opens the up the possibility of quantum experiments on multilayered arrays of trapped ions. Other platforms such as neutral atoms in tweezers and optical lattices, and polar molecules, have already demonstrated multilayer arrays, whereas large-scale multilayer crystals of trapped ions have been elusive so far. We show that the bilayer geometry opens up a range of capabilities such as the ability to have tunable bilayer Ising models and chiral spin exchange models, which can aid in studying novel quantum sensing protocols as well as in quantum simulation of models of relevance to condensed matter physics. You can find our paper here, and a popular summary of our work here and here. 

Quantum synchronization

Synchronization is a ubiquitous phenomenon in nature and refers to the ability of self-sustained oscillators to lock their phase relative to each other or to an external drive. Quantum synchronization is a recent field of study aimed at exploring how systems with low occupation numbers or with a finite number of levels synchronize. While there are many notions of quantum synchronization, we have so far explored how quantum self-sustained oscillators, i.e., quantum systems whose populations are stabilized by suitable gain and damping mechanisms,  develop coherence when subjected to a weak external perturbation that breaks the phase symmetry of the system. Examples of such oscillators include lasers and quantum van der Pol oscillators, among others. 

We recently proposed a simple two-qubit system subjected to gain and loss channels on each qubit as a composite system that exhibits rich synchronization behavior. Interestingly, we found phase locking and synchronization features that manifest only when one of the qubits is gain dominated and the other is loss dominated. We also proposed an experimental realization using transmon qubits coupled to each other and to auxiliary resonators, as shown in the image above. Our work can be found here.

More recently, we demonstrated a fruitful connection between quantum synchronization and quantum sensing: We showed that the quantum Fisher information framework constitutes a powerful toolbox to quantify and analyze quantum synchronization. Conversely, quantum synchronizing systems can be naturally interpreted as dissipative quantum sensors, opening the domain of quantum sensing as a broad application area for quantum synchronizing systems. Our preprint can be found here.

High-dimensional Multipartite Entanglement

While most of today's quantum information experiments utilize qubits, a variety of systems with more than two levels are now being brought under precise quantum control. This opens the avenue to explore the entanglement of two or more qudits and how such high-dimensional multipartite entanglement can be used in applications. Large strides have been taken in this direction, especially in the photonics community, where seminal experiments have prepared and verified the entanglement structure of high-dimensional qudits encoded in photonic degrees of freedom. More recent efforts have tried to prepare analogous states using qudits encoded in real or artificial atoms (such as superconducting qutrits). However, scalable protocols to prepare such states in atomic systems are currently unknown. 

In our recent work, we proposed a novel mechanism to prepare qudit analogs of the Greenberger-Horne-Zeilinger states for an arbitrary number of qutrits and ququarts (four-level qudits). We call our mechanism as Balanced One-Axis Twisting, or BOAT in short, since it is a multilevel generalization of the celebrated one-axis twisting model that is well known in ensembles of qubits. We show how to realize BOAT in trapped ion systems and also propose an experimental protocol to verify the high-dimensional multipartite entanglement structure of the prepared states. You can find our preprint here.