Wave mixing in an optical medium is one of the fundamental nonlinear parametric processes. However, it has not yet been thoroughly studied on single atoms. This effect requires a strong coupling of atoms to propagating waves and is hard to demonstrate with natural atoms. Nevertheless, it is possible to investigate the properties of artificial superconducting atoms coupled with coplanar waveguides. We have prepared an experimental setup and developed a topology of a superconducting chip. This setup is to be used to investigate the mixing of superpositions of the vacuum and single-photon states with coherent pulses on single atoms. An on-chip single-photon source is proposed to generate such states.
Wave mixing in an optical medium is one of the fundamental nonlinear parametric processes. However, it has not yet been thoroughly studied on single atoms. This effect requires a strong coupling of atoms to propagating waves and is hard to demonstrate with natural atoms. Nevertheless, it is possible to investigate the properties of artificial superconducting atoms coupled with coplanar waveguides. We have prepared an experimental setup and developed a topology of a superconducting chip. This setup is to be used to investigate the mixing of superpositions of the vacuum and single-photon states with coherent pulses on single atoms. An on-chip single-photon source is proposed to generate such states.
Superconducting quantum systems (artificial atoms) have been recently successfully used to demonstrate on-chip effects of quantum optics with single atoms in the microwave range. In particular, a well-known effect of four wave mixing could reveal a series of features beyond classical physics, when a non-linear medium is scaled down to a single quantum scatterer. Here we demonstrate the phenomenon of quantum wave mixing (QWM) on a single superconducting artificial atom. In the QWM, the spectrum of elastically scattered radiation is a direct map of the interacting superposed and coherent photonic states. Moreover, the artificial atom visualises photon-state statistics, distinguishing coherent, one- and two-photon superposed states with the finite (quantised) number of peaks in the quantum regime. Our results may give a new insight into nonlinear quantum effects in microwave optics with artificial atoms.
The realization of a quantum network composed of quantum nodes which process quantum fields and quantum channels to transfer quantum information has recently been proposed. In recent years, fundamental experiments produced by superconducting circuits suggest that they are promising candidates for realization of a quantum network. Superconducting circuit QED can act as quantum nodes, which can be linked by quantum channels, to transfer flying microwave photons (quantum information) from site to site on chip with high fidelity. Therefore, controlling the propagating microwave photons on chip is an essential step towards realization of a quantum network.In this thesis, we demonstrate a specific quantum node, namely the single photon router. The active element of the router is a single three-level artificial atom, a superconducting transmon type qubit, strongly coupled to a superconducting 1D transmission line. Strong coupling between the artificial atom and propagating microwave photons, revealed in high degree scattering of the resonance waves, has been observed. By exploiting the phenomenon of electromagnetically induced transparency (EIT), we can route a single photon signal from an input port to either of two output ports with an on-off ratio of approximately 90%. The switching time of the router is shown to be a few nanoseconds, consistent with theoretical expectations and the device parameters. Besides the router, we also observed some fundamental phenomenon of single atom, such as strong nonlinearity, anomalous dispersion and the Mollow Triplet.This thesis describes the motivation, theoretical background, design, implementation and the measurement results.
The field of cavity quantum electrodynamics (cavity QED) studies the interaction between light and matter on a fundamental level: a single atom interacts with a single photon. If the atom-photon coupling is larger than any dissipative effects, the system enters the strong-coupling limit. A peculiarity of this regime is the possibility to form coherent superpositions of light and matter excitations - a kind of 'molecule' consisting of an atomic and a photonic contribution. The novel research field of circuit QED extends cavity QED concepts to solid-state based system. Here, a superconducting quantum bit is coupled to an on-chip superconducting one-dimensional waveguide resonator. Owing to the small mode-volume of the resonant cavity, the large dipole moment of the 'artificial atom' and the enormous engineering potential inherent to superconducting quantum circuits, remarkable atom-photon coupling strengths can be realized. This thesis describes the theoretical framework, the development of fabrication techniques and the implementation of experimental characterization techniques for superconducting quantum circuits for circuit QED applications. In particular, we study the interaction between superconducting flux quantum bits and high-quality coplanar waveguide resonators in the strong-coupling limit. Furthermore, we report on the first experimental realization of a circuit QED system operating in the ultrastrong-coupling regime, where the atom-photon coupling rate reaches a considerable fraction of the relevant system frequencies. In these experiments we could observe phenomena that can not be explained within the renowned Jaynes-Cummings model.
Quantum optics in superconducting circuits, known as circuit QED, studies the interaction of photons at microwave frequencies with artificial atoms made of Josephson junctions. Although quite young, remarkable progress has been made in this field over the past decade, especially given the interest in building a quantum computer using superconducting circuits. In this thesis based on the appended papers, we look at generation, engineering and detection of microwave photons using superconducting circuits. We do this by taking advantage of the strong coupling, on-chip tunability and huge nonlinearity available in superconducting circuits. First, we present the strong photon-photon interaction measured experimentally, as shown in the giant cross-Kerr effect. In this work, conditional phase shift of about 20 degrees per photon was measured between two coherent fields at single photon level. Given this strong interaction, we propose and analyze a cascaded setup based on the cross-Kerr effect to detect itinerant microwave photons, a long outstanding problem with only recent experimental realizations. We show that a nondestructive detection of microwave photons is possible with few cascaded transmons. The on-chip tunability of Superconducting Quantum Interference Device (SQUID) is exploited to create a tunable superconducting resonator in the next presented experimental work. Finally, we show that by placing the atom at the end of a transmission line, microwave photons can be generated efficiently and on-demand. We also present a setup that can generate the photons in arbitrary wave packets.
Abstract Sub-wavelength arrays of atoms exhibit remarkable optical properties, analogous to those of phased array antennas, such as collimated directional emission or nearly perfect reflection of light near the collective resonance frequency. We propose to use a single-sheet sub-wavelength array of atoms as a switchable mirror to achieve a coherent interface between propagating optical photons and microwave photons in a superconducting coplanar waveguide resonator. In the proposed setup, the atomic array is located near the surface of the integrated superconducting chip containing the microwave cavity and optical waveguide. A driving laser couples the excited atomic state to Rydberg states with strong microwave transition. Then the presence or absence of a microwave photon in the superconducting cavity makes the atomic array transparent or reflective to the incoming optical pulses of proper frequency and finite bandwidth.
We address recent advances in quantum optics with propagating microwaves\nin superconducting circuits. This research field exploits on the fact that the coupling between a superconducting artificial atom and propagating microwave photons in a one-dimensional (1D) open transmission line can be made strong enough to observe quantum effects, without using any cavity to confine the microwave photons.\nWe embed an artificial atom, a superconducting transmon qubit, in a 1D open\ntransmission line and investigate the scattering properties of coherent microwaves. When an input coherent state, with an average photon number much less than 1, is on resonance with the artificial atom, we observe extinction of up to 99% in the forward propagating field. We observe the strong nonlinearity of the artificial atom and under strong driving we observe the Mollow triplet. We also study the statistics of the reflected and transmitted beams, which are predicted to be nonclassical states. In particular, we demonstrate photon antibunching in the reflected beam by measuring the second-order correlation function. By applying a second control tone, we observe the Autler-Townes splitting and a giant cross-Kerr effect.\nFurthermore, we demonstrate fast operation of a single-photon router using\nthe Autler-Townes splitting. This device provides important steps towards the realization of a quantum network. This thesis describes the motivation, theoretical background, design, implementation and measurement results.