JQI-QuICS-CMTC Seminar

The standard circuit model for quantum computation presumes the ability to directly perform gates between arbitrary pairs of qubits, which is unlikely to be practical for large-scale experiments. Power-law interactions with strength decaying as 1/r^α in the distance r provide an experimentally realizable resource for information processing, whilst still retaining long-range connectivity. We leverage the power of these interactions to  implement a fast quantum fanout gate with an arbitrary number of targets.

Junctions of more than two superconducting terminals are required for implementing braiding operations on Majorana fermions. Moreover, such multi-terminal Josephson Junctions (JJ) were predicted to support topological state and host zero-energy quasiparticles. Unlike conventional two-terminal JJs where the value of critical current is a number, the multi-terminal JJs exhibit a novel feature – the critical current contour (CCC).

The field of quantum Hamiltonian complexity lies at the intersection of quantum many-body physics and computational complexity theory, with deep implications to both fields. The main object of study is the LocalHamiltonian problem, which is concerned with estimating the ground-state energy of a local Hamiltonian. A major challenge in the field is to understand the complexity of the LocalHamiltonian problem in more physically natural parameter regimes.

Confinement is a ubiquitous mechanism in nature, whereby particles feel an attractive force that increases without bound as they separate. A prominent example is color confinement in particle physics, in which baryons and mesons are produced by quark confinement. Analogously, confinement can also occur in low-energy quantum many-body systems when elementary excitations are confined into bound quasiparticles. We report the observation of magnetic domain wall confinement in an interacting spin chain with a trapped-ion quantum simulator.

Simulating the dynamics of quantum systems is an important application of quantum computers and has seen a variety of implementations on current hardware. We show that by introducing quantum gates implementing unitary transformations generated by the symmetries of the system, one can induce destructive interference between the errors from different steps of the simulation, effectively giving faster quantum simulation by symmetry protection.

The interaction of a single photon with an individual two-level system is the textbook example of quantum electrodynamics. Achieving strong coupling in this system has so far required confinement of the light field inside resonators or waveguides. Experiments with Rydberg superatoms [1,2] have demonstrated the ability to realize strong coupling to a propagating light pulse containing only a few photons in free space.

We are in the midst of a second quantum revolution fueled by the remarkable quantum mechanical properties of physical systems. Therefore, characterization and engineering of these quantum systems is vitally important in emerging quantum optical science and technology. The Wigner quasi-probability distribution function provides such a characterization.

Density matrices represent our knowledge about quantum systems. We can use them to calculate any physical property of quantum systems via the Born rule. Since the density matrix grows exponentially with the number of qubits, already at about 50 qubits, simply writing and storing the density matrix in a classical computer, becomes impossible, let alone calculating anything with it.

Quantum photonics provides a powerful toolbox with vast applications ranging from quantum simulation, photonic information processing, all optical universal quantum computation, secure quantum internet as well as quantum enhanced sensing.

The AdS/CFT correspondence is a concrete instance of holographic duality, where a bulk theory of quantum gravity in d+1 dimensions can emerge from a conformal field theory (CFT) in d dimensions. In particular, we expect the semi-classical spacetime of d+1 dimensions to emerge from the entanglement patterns of certain quantum states in the CFT. Therefore, it is crucial to understand what kind of states encode such spacetime geometries and how to explicitly reconstruct these geometries from quantum entanglement.