Generation, Manipulation, and Detection of Complex States of Microwave Radiation

Emily Pritchett, Luke C. G. Govia, Frank K. Wilhelm

Ida-Maria Svensson

In this thesis I present different types of manipulations of microwave fields using tunable superconducting resonators. A resonator is made tunable by adding one or more superconducting quantum interference devices, SQUIDs. The SQUID consists of a superconducting loop with two Josephson junctions and acts as a tunable nonlinear inductor. Modulation of the SQUID nonlinearity can be performed to induce different types of non-trivial oscillator dynamics. The first project I present is on subharmonic oscillations. Here, the SQUID in a tunable resonator is driven with an external signal at an integer multiple of the frequency w. When w is placed slightly below the first resonator mode, I show generation of radiation at w, which is known as frequency down-conversion. In my measurements, subharmonic oscillations have been detected from period doubling up to period quintupling. For the specific case of period tripling, theory is developed and I show good agreement between theory and experiments. The second project of the thesis is on a doubly tunable resonator. Here, I show creation of a superconducting resonator with two independently tunable boundary conditions. The idea with this system is to operate the resonator in a breathing or a translational mode and compare the two. For static dc magnetic flux the performance is very good. As a second step, I perform fast modulation of both SQUIDs to generate radiation. Even though some of the measurement results are promising, I also show some contradicting observations. These indicate that the actual modulation mechanism of the SQUID is not pumping of the magnetic flux in the SQUID loop as intended, but rather direct current driving of the SQUID. However, the system remains a promising idea for microwave manipulation and creation of interesting non-classical states. As a possible application of the doubly tunable resonator, I present a theory proposal on how to use it for measurements on relativistic effects. By using the tunability of the resonator boundary conditions, the resonator can simulate a space rocket and time dilation could be measured. However, due to the crosstalk problems in the doubly tunable resonator this experiment was never realized. Finally, I finish the thesis by presenting a design for a tunable microwave coupling. Papers E and F show a high on-off ratio for the coupler and demonstrate how it can be used for storage of microwave signals. Furthermore, the tunable coupler can be used to shape a microwave signal by tuning the strength of the coupling.

Manuel A. Castellanos-Beltran, M. P. DeFeo, Adam J. Sirois +4 more

Andreas J. Wallraff

Using modern micro and nano-fabrication techniques combined with superconducting materials we realize quantum electronic circuits in which we create, store, and manipulate individual microwave photons. The strong interaction of photons with superconducting quantum two-level systems allows us to probe fundamental quantum effects of microwave radiation and also to develop components for applications in quantum technology. Previously we have realized on-demand single photon sources which we have characterized using correlation function measurements [1] and full quantum state tomography [2]. For this purpose we have developed efficient methods to separate the quantum signals of interest from the noise added by the linear amplifiers used for quadrature amplitude detection [3]. We now regularly employ superconducting parametric amplifiers [4] to perform nearly quantum limited detection of propagating electromagnetic fields. These enable us to probe the entanglement which we generate on demand between stationary qubits and microwave photons freely propagating down a transmission line [5]. Using two independent microwave single photon sources, we have recently performed Hong-Ou-Mandel experiments at microwave frequencies [6] and have probed the coherence of two-mode multi-photon states at the out-put of a beam-splitter. The non-local nature of such states may prove to be useful for distributing entanglement in future small-scale quantum networks.

Mahajan Aarushe

Quantum sensing is a creative application of quantum technology which is opening new horizons in order to make sensitive measurements even below the Standard Quantum Limit (SQL). In order to achieve this, an exclusive phenomenon of Quantum Entanglement is widely used for various tasks such as target detection, providing high resolution of the target, encryption of data and quantum teleportation which may seem to be impracticable. Moreover, the field of quantum technology has witnessed appreciable progress by using microwaves than optical photons. Microwave photons as efficient they are can also be used in a system for obtaining quantum information about the surroundings. \nIn this work, an idea is proposed to make use of microwaves as a source for the photonic sensor network. Squeezed microwave states are used for the generation of microwave photons which are used in their entangled state distributed among sensors and thereafter detected by the homodyne detector. Here, the use of hybrid coupler is also made to act as beam splitters forming the Continuous Variable multipartite entanglement of the microwave photons for further detection. Another idea is proposed to use a system for generation and detection of microwave photons in order to have application in quantum sensing field. In this for the generation part Nitrogen Vacancy (NV) centers defect is used as these NV centers with electrons can be used to manipulate microwaves in order to emit photons which carry quantum information about the environment. Then these emitted photons can be detected using a system formed by qubits and resonators which are coupled in a peculiar way using the dissipation engineering to detect itinerant photons.