28-01-2013, 11:54 AM
Atomic Physics with a Superconducting Artificial Atom
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ABSTRACT
Superconducting persistent-current qubits are quantum-coherent artificial atoms with multiple energy levels. Control sequences comprising harmonic pulses modulate the qubit "transversally" (e.g., Rabi oscillations) and "longitudinally" (e.g., Landau-Zener transitions) to drive transitions between energy levels and probe the atom's coherence.
This seminar presents recent experimental demonstrations of coherence in superconducting artificial atoms under transverse and longitudinal driving conditions. Using a long-lived aluminum qubit (T1=10 µs, T2Echo=23 µs), MIT Lincoln Laboratory performed Rabi, Ramsey, and dynamical decoupling pulse sequences (e.g., spin echo, CP, and CPMG) to probe the coherence and noise generators in our artificial atom as a function of quantization axis [1]. In other experiments with a niobium qubit, the Laboratory demonstrated several examples of large-amplitude longitudinal driving, including Mach-Zehnder-type interferometry of n- photon transistions (n = 1…50) [1]; microwave-induced cooling [2], by which the Laboratory achieved effective qubit temperatures <3 mK; and amplitude spectroscopy [3], a spectroscopy approach that monitors the system response to amplitude rather than frequency. This allowed us to probe the energy spectra of our artificial atom from 0.01–120 GHz, while driving it at a fixed frequency 0.16 GHz. These experiments exhibit a remarkable agreement with theory and are extensible to other solid-state qubit modalities. In addition to our interest in these techniques for fundamental studies of quantum coherence in strongly driven solid-state systems, it is anticipated they will find application to nonadiabatic qubit control and state-preparation methods for quantum information science and technology.
[attachment=48570]
ABSTRACT
Superconducting persistent-current qubits are quantum-coherent artificial atoms with multiple energy levels. Control sequences comprising harmonic pulses modulate the qubit "transversally" (e.g., Rabi oscillations) and "longitudinally" (e.g., Landau-Zener transitions) to drive transitions between energy levels and probe the atom's coherence.
This seminar presents recent experimental demonstrations of coherence in superconducting artificial atoms under transverse and longitudinal driving conditions. Using a long-lived aluminum qubit (T1=10 µs, T2Echo=23 µs), MIT Lincoln Laboratory performed Rabi, Ramsey, and dynamical decoupling pulse sequences (e.g., spin echo, CP, and CPMG) to probe the coherence and noise generators in our artificial atom as a function of quantization axis [1]. In other experiments with a niobium qubit, the Laboratory demonstrated several examples of large-amplitude longitudinal driving, including Mach-Zehnder-type interferometry of n- photon transistions (n = 1…50) [1]; microwave-induced cooling [2], by which the Laboratory achieved effective qubit temperatures <3 mK; and amplitude spectroscopy [3], a spectroscopy approach that monitors the system response to amplitude rather than frequency. This allowed us to probe the energy spectra of our artificial atom from 0.01–120 GHz, while driving it at a fixed frequency 0.16 GHz. These experiments exhibit a remarkable agreement with theory and are extensible to other solid-state qubit modalities. In addition to our interest in these techniques for fundamental studies of quantum coherence in strongly driven solid-state systems, it is anticipated they will find application to nonadiabatic qubit control and state-preparation methods for quantum information science and technology.