The method of stimulated Raman adiabatic passage is applied in order to coherently manipulate a three-level superconducting quantum interference device quantum bit with two microwave pulses. Simulations indicate that this method has the potential to allow for efficient control of the system for a wide range of pulse parameters.
The adiabatic manipulation of quantum states is a powerful technique that opened up new directions in quantum engineering--enabling tests of fundamental concepts such as geometrical phases and topological transitions, and holding the promise of alternative models of quantum computation. Here we benchmark the stimulated Raman adiabatic passage for circuit quantum electrodynamics by employing the first three levels of a transmon qubit. In this ladder configuration, we demonstrate a population transfer efficiency >80% between the ground state and the second excited state using two adiabatic Gaussian-shaped control microwave pulses. By doing quantum tomography at successive moments during the Raman pulses, we investigate the transfer of the population in time domain. Furthermore, we show that this protocol can be reversed by applying a third adiabatic pulse, we study a hybrid nondiabatic-adiabatic sequence, and we present experimental results for a quasi-degenerate intermediate level.
Adiabatic manipulation of the quantum state is an essential tool in modern quantum information processing. Here, we demonstrate the speedup of the adiabatic population transfer in a three-level superconducting transmon circuit by suppressing the spurious nonadiabatic excitations with an additional two-photon microwave pulse. We apply this superadiabatic method to the stimulated Raman adiabatic passage, realizing fast and robust population transfer from the ground state to the second excited state of the quantum circuit.
We propose an approach for the arbitrary rotation of a three-level superconducting quantum interference device (SQUID) qubit and describe a strategy for the creation of coherence transfer and entangled states between two three-level SQUID qubits. The former is succeeded by exploring the coupled-uncoupled states of the system when irradiated with two microwave pulses, and the latter is succeeded by placing the SQUID qubits into a microwave cavity and used adiabatic passage methods for their manipulation.
Stimulated Raman adiabatic passage (STIRAP) is a widely-used technique of coherent state-to-state manipulation for many applications in physics, chemistry, and beyond. The adiabatic evolution of the state involved in STIRAP, called adiabatic passage, guarantees its robustness against control errors, but also leads to problems of low efficiency and decoherence. Here we propose and experimentally demonstrate an alternative approach, termed stimulated Raman "user-defined" passage (STIRUP), where a parameterized state is employed for constructing desired evolutions to replace the adiabatic passage in STIRAP. The user-defined passages can be flexibly designed for optimizing different objectives for different tasks, e.g. minimizing leakage error. To experimentally benchmark its performance, we apply STIRUP to the task of coherent state transfer in a superconducting Xmon qutrit. We found that STIRUP completed the transfer more then four times faster than STIRAP with enhanced robustness, and achieved a fidelity of 99.5%, which is the highest among all recent experiments based on STIRAP and its variants. In practice, STIRUP differs from STIRAP only in the design of driving pulses; therefore, most existing applications of STIRAP can be readily implemented with STIRUP.
In circuit quantum electrodynamics the coherence of Cooper pairs in superconductors is employed to create macroscopic electric circuits with quantized energy levels. Such circuits can be coupled with each other and exploited as building blocks of a quantum computer. Accurate and robust control of the quantum state in the circuits is a central condition for the operation of the quantum computer and one of the prerequisites for the implementation of complex algorithms used in quantum information processing, such as quantum error correction. In this thesis adiabatic control in circuit quantum electrodynamics is investigated with the focus on manipulating three-level systems. \n \nIn adiabatic control the eigenstates of the system are slowly modified by changing the external control parameters, which govern the evolution of the system. If the changes in the parameters are slow enough, the state of the system follows the eigenstates in the adiabatic basis, thereby realizing the intended operation. The advantage of adiabatic control is its inherent robustness to small errors or noise in the control parameters; the result of the state manipulation only depends on the asymptotic values of the control parameters, but not on their exact values during the process. \n \nShortcuts to adiabaticity can be used to speed up the otherwise slow adiabatic control by introducing a correction pulse that compensates the diabatic losses during the state manipulation. This allows one to overcome the limitation on the speed of the protocol but simultaneously reduces the method's robustness to the variations in the control parameters. If the level of noise in the control parameters is known, using the shortcut it is possible to find the optimal level of robustness which is required to mitigate the noise. \n \nCircuit quantum electrodynamics offers a perfect experimental platform for investigating quantum control due to the possibility of realizing complicated control schemes using microwave electronics. With commercially available digital-to-analog converters the control signals can be digitally created, which enables accurate and coherent control of the quantum circuit. \n \nIn this thesis both theoretical and experimental results on adiabatic control applied to superconducting transmon circuits are presented. It is shown that stimulated Raman adiabatic passage can be used for population transfer in a three-level transmon, which can be further improved using shortcuts to adiabaticity. Furthermore, a scheme for implementing robust superadiabatic rotation gates in transmon is proposed. Finally, it is demonstrated that superconducting qubit can be used as an ultra-sensitive detector of magnetic flux.