Observation of macroscopic Landau-Zener transitions in a superconducting device

Izmalkov, A.; Grajcar, M.; Il’ichev, E.; Oukhanski, N.; Wagner, Th.; Meyer, H.‐G.; Krech, W.; Amin, M. H. S.; Brink, Alec Maassen van den; Zagoskin, A. M.

doi:10.1209/epl/i2003-10200-6

Cited by 66 publications

(52 citation statements)

References 13 publications

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“…1-4). Superconducting qubits being quantum mesoscopic objects present possibility to realize several unique quantum phenomena, such as entanglement [5,6], Rabi oscillations [7][8][9][10][11][12], spin echo and Ramsey fringes [13,14], Landau-Zener-Stückel-berg interferometry [15][16][17][18][19], etc. Presently large interest brings over to the problem of the behavior of such artificial atoms in a quantized electromagnetic field in the frame of so-called circuit quantum electrodynamics (CQED) [20].…”

Section: Introductionmentioning

confidence: 99%

Quantum behavior of a flux qubit coupled to a resonator

Omelyanchouk

Shevchenko

Greenberg

et al. 2010

Low Temperature Physics

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The detailed theory for the system of a superconducting qubit coupled to the transmission line resonator is presented. We describe the system by solving analytically and numerically the master equation for the density matrix, which includes dissipative Lindblad term. We calculate the transmission coefficient, which provides the way to probe the dressed states of the qubit. The theoretical results are related to the experiment with the intermediate coupling between the qubit and the resonator, when the coupling energy is of the same order as the qubit relaxation rate.

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Section: Introductionmentioning

confidence: 99%

Quantum behavior of a flux qubit coupled to a resonator

Omelyanchouk

Shevchenko

Greenberg

et al. 2010

Low Temperature Physics

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“…A number of recent experiments have also examined superconducting circuits under extreme driving [10,11,12]. These experiments were interpreted in terms of interference between multiple Landau-Zener transitions in the qubits.…”

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Coherence Times of Dressed States of a Superconducting Qubit under Extreme Driving

et al. 2007

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In this work, we measure longitudinal dressed states of a superconducting qubit, the single Cooperpair box, and an intense microwave field. The dressed states represent the hybridization of the qubit and photon degrees of freedom, and appear as avoided level crossings in the combined energy diagram. By embedding the circuit in an rf oscillator, we directly probe the dressed states. We measure their dressed gap as a function of photon number and microwave amplitude, finding good agreement with theory. In addition, we extract the relaxation and dephasing rates of these states.When matter and light interact at the quantum level, in the form of atoms and photons, it is often no longer possible to clearly distinguish the individual contribution of each to the overall behavior of the system. This mixing of the aspects of light and matter can then be described in terms of dressed states of the atoms and photons [1]. These dressed states have become an essential concept in many fields of physics. Recently, they have also been invoked to explain the behavior of electrical circuits operating in the quantum regime [2,3]. In this context, known as circuit quantum electrodynamics (QED), we directly measure a class of states, longitudinal dressed states (LDS), that have received little experimental attention in the past. We create these states by illuminating an artificial atom made from a nanofabricated superconducting circuit with microwave photons. We then observe the interaction of the dressed states and a radiofrequency (rf) oscillator. This measurement scheme allows us to directly map the dressed energy diagram and extract the relaxation and dephasing times of the states. LDS are the natural description of a strongly driven superconducting quantum bit (qubit), and may have applications in the field of quantum information processing.Significant advances have been made in the development of engineered systems that exhibit coherent quantum properties. In the new field of circuit QED, these artificial atoms have recently been used to not only reproduce results of atomic physics and quantum optics, but to explore regimes previously inaccessible to traditional experiments [4]. Here, we use circuit QED techniques to directly study LDS over a wide range of drive strengths, including the extreme driving regime where the driving field is much stronger than the polarizing field. In atomic systems, the field strengths required for this are technically difficult to achieve and often exceed the ionization threshold of the atoms. The field geometry studied is also unusual. In a typical atomic experiment, a strong, static field is used to polarize the atomic spins under study. A relatively weak ac field, aligned perpendicular to the polarizing field, is then used to drive the spins. This transverse field geometry in fact implies that the atomic and photon spins are aligned, leading to a variety of selection rules based on the conservation of angular momentum. In our experiment, the driving field is aligned parallel to the polarizing fi...

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“…In this case, the transitions occur via the Landau-Zener (LZ) process at a level crossing [11,12]. Acting as a coherent beamsplitter, LZ transitions create a quantum superposition of the ground and excited states and, upon repetition, induce quantum mechanical interference.…”

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confidence: 99%

Coherent Quasiclassical Dynamics of a Persistent Current Qubit

Berns

Oliver

Valenzuela³

et al. 2006

Phys. Rev. Lett.

121

190

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A new regime of coherent quantum dynamics of a qubit is realized at low driving frequencies in the strong driving limit. Coherent transitions between qubit states occur via the Landau-Zener process when the system is swept through an energy-level avoided crossing. The quantum interference mediated by repeated transitions gives rise to an oscillatory dependence of the qubit population on the driving field amplitude and flux detuning. These interference fringes, which at high frequencies consist of individual multiphoton resonances, persist even for driving frequencies smaller than the decoherence rate, where individual resonances are no longer distinguishable. A theoretical model that incorporates dephasing agrees well with the observations. PACS numbers: 03.67. Lx,03.65.Yz,85.25.Cp,85.25.Dq Macroscopic quantum systems coherently driven by external fields provide new insights into the fundamentals of quantum mechanics and hold promise for applications such as quantum computing [1]. Superconducting Josephson devices are model quantum systems that can be manipulated by RF driving fields [2], and recent years have seen rapid progress in the understanding of their quantum dynamics [3,4,5,6,7,8,9,10]. Quantum coherence of these systems can be probed by temporal Rabi oscillations [3,6,7,8,9,10]. There, the drivingfield frequency ν equals the energy level separation ∆E, and the population of the two levels oscillates at a frequency ω R much smaller than ∆E. In the weak driving limit,hω R ≈ A ≪ ∆E = hν, where A is the driving amplitude parameterized in units of energy.Coherent quantum dynamics can also be investigated at driving frequencies much less than ∆E, and at strong driving amplitude A ≈ ∆E ≫ hν. In this case, the transitions occur via the Landau-Zener (LZ) process at a level crossing [11,12]. Acting as a coherent beamsplitter, LZ transitions create a quantum superposition of the ground and excited states and, upon repetition, induce quantum mechanical interference. The latter leads to Stueckelberg-type oscillations [13,14] in analogy to a Mach-Zehnder (MZ) interferometer [15,16]. These oscillations are also related to photoassisted transport [17,18,19] and Rabi oscillations observed in the multiphoton regime [6,20]. MZ-type interference is a unique signature of temporal coherence complementary to Rabi oscillations, with the time between sequential LZ transitions clocking the dynamics similarly to Rabi pulse width.In this Letter, we report a new quasiclassical regime which exhibits coherence even at driving frequencies low compared to dephasing rate, νT 2 < ∼ 1 [21]. This occurs because the interval between consecutive LZ transitions, relevant for MZ interference, is only a fraction of the driving field period. We investigate the crossover between the multiphoton and quasiclassical regimes, demonstrating that coherent MZ-type interference fringes in the qubit population persist for frequencies νT 2 < ∼ 1 even though individual multiphoton resonances can no longer be resolved. This behavior should be contrasted ...

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Observation of macroscopic Landau-Zener transitions in a superconducting device

Cited by 66 publications

References 13 publications

Quantum behavior of a flux qubit coupled to a resonator

Quantum behavior of a flux qubit coupled to a resonator

Coherence Times of Dressed States of a Superconducting Qubit under Extreme Driving

Coherent Quasiclassical Dynamics of a Persistent Current Qubit

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