QST Experiment: Quantum Hardware – Lecture

Lecture Content

This course provides an overview of various different physical implementations of quantum systems, which are promising for future applications of quantum technologies. Starting with a brief review of key physical concepts and applications, we first focuse on light-matter interaction, providing the basic concepts of cavity and circuit quantum electrodynamics (QED) as well as the essential models to describe the quantum systems discussed later. Then, various different experimental approaches to realize superconducting and semiconducting quantum bits are introduced. This includes the techniques for control, manipulation and readout of qubits, the concepts for single and two-qubit gates and the routes to build large quantum processors based on them. In the last part, the foundations of quantum sensing are introduced. This includes the discussion of noise sources and the fundamental limits of sensitivity (standard quantum limit and beyond). It time permits, the implementation of quantum sensors via opto-mechanical systems and color centers in semiconductors are discussed.

Introduction, Overview and Motivation

• What is “Quantum 1.0”, what is “Quantum 2.0”?
• Quantum two-level system, quantum harmonic oscillator
• Superposition, entanglement, relaxation and dephasing (examples NMR, ESR)
• Quantum vs. classical information
• Potential applications: computing, simulation, sensing, cryptography

Light-Matter Interaction

Light

• Quantization of the electromagnetic field
• Thermal, coherent, Fock states (photon statistics, correlations, bunching, ...)
• Photon boxes (mode volume, vacuum field, …)
• Sources and detectors (optical vs microwave, single photons, coherent light, ..)
• Entangled photons

Matter

• Natural and artificial atoms, realization of quantum two-level systems
• Size of dipole moments

Light-matter interaction

• Semi-classical light-matter interaction
• Jaynes-Cummings model, Rabi model
• Cavity and circuit electrodynamics (cooperativity, coupling strength, strong vs. ultra-strong coupling)
• AC Stark effect

Experimental tools and methods

Superconducting Quantum Circuits

• Superconducting resonators (1D vs 3D, quality factor)
• Superconducting qubits as nonlinear harmonic oscillators (Josephson junction as dissipationless nonlinear inductance)
• Engineering of Qubit Hamiltonian (Interaction strength, Anharmonicity, Decoherence)
• Single and two-qubit gates
• Control, manipulation and readout

Semiconductor Quantum Circuits

• Resonators
• Semiconductor quantum bits (III-V quantum dots, donors and defects)
• Interaction strength, anharmonicity, decoherence & dephasing
• Single and two-qubit gates
• Control, manipulation, readout

Atoms, Ions and Quantum Gases

• Generation and characterization: experimental techniques
• Quantum simulation / computing with trapped ions / atoms
• Optical lattices
• Bose-/Fermi-Hubbard model

Quantum Sensing

• Limitation of sensitivity, noise sources, noise power spectral density, amplifiers
• Standard quantum limit (SQL) of sensing and measurement
• Optomechanics
• Quantum sensing with NV center spin qubits, SQL for sensing with spins
• Quantum sensing beyond the SQL: squeezed light or the implementation of quantum non-demolition measurement protocols

Prerequisites:

Basic knowledge in Atomic Physics and Quantum Mechanics I.