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Raman coherence effects in a superconducting Jaynes-Cummings system

Novikov, Sergey

Published Jan 1, 2015• 1 citation
Publisher

Abstract

This dissertation describes a study of Raman coherence effects using superconducting quantum circuits. Raman coherence can occur in a three-level system driven by two coherent electromagnetic fields. In a suitable system with a metastable state, the effect is typically manifest as coherent population trapping (CPT) and electromagnetically induced transparency (EIT). I derive the theoretical framework and show experimentally that in the case of a cascade three-level system based on transmon superconducting qubit states, an effect known as the Autler-Townes doublet (ATD), rather than CPT or EIT, occurs. I propose, model, and implement a quasi- system made of combined transmon-cavity levels, which has a meta-stable state required for CPT and EIT. I measure CPT, and demonstrate coherence of the dark state in the time domain. Instead of EIT, I observe a new phenomenon – electromagnetically suppressed transmission (EST). The large negative dispersion accompanying EST leads to superluminal pulse propagation in the system. My results suggest that quantum superconducting circuits provide a viable platform for studying quantum optics of multi-level systems.

DOI
10.13016/m2td1m

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This dissertation describes a study of Raman coherence effects using superconducting quantum circuits. Raman coherence can occur in a three-level system driven by two coherent electromagnetic fields. In a suitable system with a metastable state, the effect is typically manifest as coherent population trapping (CPT) and electromagnetically induced transparency (EIT). I derive the theoretical framework and show experimentally that in the case of a cascade three-level system based on transmon superconducting qubit states, an effect known as the Autler-Townes doublet (ATD), rather than CPT or EIT, occurs. I propose, model, and implement a quasi- system made of combined transmon-cavity levels, which has a meta-stable state required for CPT and EIT. I measure CPT, and demonstrate coherence of the dark state in the time domain. Instead of EIT, I observe a new phenomenon – electromagnetically suppressed transmission (EST). The large negative dispersion accompanying EST leads to superluminal pulse propagation in the system. My results suggest that quantum superconducting circuits provide a viable platform for studying quantum optics of multi-level systems.
The phenomenon of coherent population trapping (CPT) of an atom (or solid state "artificial atom"), and the associated effect of electromagnetically induced transparency (EIT), are clear demonstrations of quantum interference due to coherence in multilevel quantum systems. We report observation of CPT in a superconducting phase qubit by simultaneously driving two coherent transitions in a Lambda-type configuration, utilizing the three lowest lying levels of a local minimum of a phase qubit. We observe 60(+/-7)% suppression of the excited state population under conditions of CPT resonance. We present data and matching theoretical simulations showing the development of CPT in time. Finally, we used the observed time dependence of the excited state population to characterize quantum dephasing times of the system.
We have created a quantum three-level ladder system with the cavity dispersive energy level in a superconducting circuit quantum electrodynamics system consisting of a transmon qubit and a cavity, and have directly observed the Autler-Townes splitting effect instead of representing it by the probability of the qubit being at each level. A coupler tone is applied on the transition between the second excited state of transmon and cavity dispersive level, while the cavity spectrum is probed. A doublet transmission and anormalous dispersion spectrum of the cavity level is clearly shown. The inverse Fourier transform of cavity spectrum indicates that there is a quantum coherence Rabi oscillation of the populations between cavity and qubit.
The quantum coherence phenomenon of electromagnetically induced transparency (EIT) is observed in a three-level system composed of an excited state and two coherent superpositions of the two ground-state levels. This peculiar ground state basis is composed of the so-called bright and dark states of the same atomic system in a standard coherent population trapping configuration. The characteristics of EIT, namely, width of the transmission window and reduced group velocity of light, in this unusual basis, are theoretically and experimentally investigated and are shown to be essentially identical to those of standard EIT in the same system.
Summary form only given. The study on the interaction between electromagnetic fields and multi-level atoms or molecules has discovered many interesting effects including electromagnetically induced transparency (EIT) enhanced dispersion with reduced absorption, and lasing without inversion. Recent interests include ultraslow group velocity of light, and superluminal light propagation. Atomic coherence created between different atomic levels plays an essential rule in these experiments. On the other hand, quantum features in the interaction between electromagnetic fields and three-level systems based on atomic coherence have attracted extensive theoretical interests. These include generation of amplitude-squeezed and quantum noise-correlated states of light with EIT, entanglement of atomic states with light fields, and quantum memory for light. According to these theoretical works, manipulation of quantum states of either light fields or atoms via atomic coherence is possible. We study quantum state manipulation of light via coherently driven Raman coherence in a /spl Lambda/-type three-level system of rubidium vapor under far off one-photon resonance condition both theoretically and experimentally.
Quantum networks will enable extraordinary capabilities for communicating and processing quantum information. These networks require a reliable means of storage, retrieval, and manipulation of quantum states at the network nodes. A node receives one or more coherent inputs and sends a conditional output to the next cascaded node in the network through a quantum channel. Here, we demonstrate this basic functionality by using the quantum interference mechanism of electromagnetically induced transparency in a transmon qubit coupled to a superconducting resonator. First, we apply a microwave bias, i.e., drive, to the qubit-cavity system to prepare a Λ-type three-level system of polariton states. Second, we input two interchangeable microwave signals, i.e., a probe tone and a control tone, and observe that transmission of the probe tone is conditional upon the presence of the control tone that switches the state of the device with up to 99.73% transmission extinction. Importantly, our electromagnetically induced transparency scheme uses all dipole allowed transitions. We infer high dark state preparation fidelities of >99.39% and negative group velocities of up to -0.52±0.09 km/s based on our data.
Atomic coherence and interference manifested by electromagentically induced transparency (EIT) and coherent population trapping (CPT) plays an important role in the current studies of atom-photon interactions and has found numerous applications in optical physics. EIT is created in a three-level atomic system by a coupling field and results in destructive interference between two excitation paths of a weak probe laser interacting with the atomic medium. This leads to suppressed linear absorption and rapidly varying atomic dispersion for the probe laser near the atomic resonance, which provides the platform for a variety of applications such as nonlinear optics at low light levels, slow light manipulation, and quantum state engineering for photons and atoms. Here we extend the simple three-level EIT system to more complicated and versatile configurations in a multi-level atomic system coupled by multiple laser fields. We show that with multiple excitation paths provided by different laser fields, phase-dependent quantum interference is induced: either constructive or destructive interference can be realized by varying the relative phases among the laser fields. Two specific examples are discussed. One is a three-level system coupled by bichromatic coupling and probe fields, in which the phase dependent interference between the resonant two-photon Raman transitions can be initiated and controlled. Another is a four-level system coupled by two coupling fields and two probe fields, in which a double-EIT configuration is created by the phase-dependent interference between three-photon and one-photon excitation processes. We analyze the coherently coupled multi-level atomic system and discuss the control parameters for the onset of constructive or destructive quantum interference. We describe two experiments performed with cold Rb atoms that can be approximately treated as the coherently coupled three-level and four-level atomic systems respectively. The experimental results show the phase-dependent quantum coherence and interference in the multi-level Rb atomic system, and agree with the theoretical calculations based on the coherently coupled three-level or four-level model system.