Harnessing the computational power of quantum systems

The behavior of physical systems at the atomic and subatomic scale is vastly different from the one at macroscopic scales we experience in our daily life. Quantum mechanics, the theory describing systems at these small scales, has many peculiar features. Most notably, quantum systems can be in a superposition of various configurations, and quantum theory only allows for probabilistic statements about the outcome of an experiment. Moreover, quantum systems can exhibit entanglement, a type of quantum correlation which has no classical counterpart. These features lead to an intricate mathematical structure of quantum mechanics, which renders the simulation of quantum many-body systems on conventional computers prohibitively demanding for many relevant problems.

During the last 50 years, it has been realized that the peculiarities of quantum systems can in fact be harnessed for information processing. In particular, it has been demonstrated both theoretically and experimentally that controllable systems whose quantum nature can be exploited are able to perform certain computational tasks more efficiently than conventional computers. While quantum computers are so far of small scale, technology is rapidly evolving and intermediate scale devices are likely to become available in the next for years.

 Bloch v1 bright  Bloch v2 bright  Bloch v3 bright

Illustration of the evolution of a single-qubit state vector on the Bloch sphere under various rotation gates. Left panel: single rotation around one axis. Center panel: combination of a rotation around the y-axis followed by a rotation around the z-axis. Right panel: combination of a rotation around the y-axis followed by a rotation around the z-axis in the presence of decoherence.

Quantum computing for quantum physics

Compared to conventional computers, quantum computers do not suffer from purely numerical limitations, thus opening up a new route to tackle problems that are inaccessible with current supercomputers. We explore this possibility, in particular in the realm of lattice field theory calculations. In close collaboration with the Lattice QCD division and the DESY Zeuthen we investigate new simulation strategies and algorithmic technologies to utilize intermediate scale quantum devices for overcoming limitations of current Monte Carlo based algorithms for lattice field theories.

Soliton

Real-time evolution for the density profile of a Bose-Einstein condensate in an optical lattice after suddenly displacing the harmonic trap holding the condensate. The movement leads to Bragg reflections which in turn create a soliton that decays over time.

 

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