The driven-damped Jaynes-Cummings model in the regime of strong coupling is found to exhibit a coexistence between the quantum photon blockaded state and a quasicoherent bright state. We characterize the slow time scales and the basin of attraction of these metastable states using full quantum simulations. This form of bistability can be useful for implementing a qubit readout scheme that does not require additional circuit elements. We propose a coherent control sequence that makes use of a simple linear chirp of drive amplitude and frequency as well as qubit frequency. By optimizing the parameters of the system and the control pulse, we demonstrate theoretically very high readout fidelities (>98%) and high contrast with experimentally realistic parameters for qubits implemented in the circuit QED architecture. Experimentally, these schemes require a following amplifier of high gain and low noise, spurring the development of quantum limited amplifiers [6]. However, the highest demonstrated fidelities to date rely on nonlinear measurement schemes with qubit-dependent latching into a clearly distinguishable state, for example, the Josephson bifurcation amplifier (JBA), as well as optimized readout of phase qubits [3,7]. For this class, during the measurement, the system evolves under the influence of time-varying external fields and nonlinear dynamics, ultimately projecting the qubit state. The space for design and control parameters is very large, and the dependence of the readout fidelity on them is highly nontrivial. Therefore, the optimization is difficult and does not posses a generic structure.We propose a coherent control-based approach to the readout of a qubit that is strongly coupled to a cavity, based on an existing cQED architecture, but not necessarily limited to it. This approach is in the spirit of the latching readout schemes, but it differs in that the source of the nonlinearity is the Jaynes-Cummings (JC) interaction. When the qubit is brought into resonance with the cavity mode, the strong anharmonicity of the JC ladder of dressed states can prevent the excitation of the system even in the presence of a strong drive, a quantum phenomenon known as photon blockade [8]. However, due to fact that the JC anharmonicity is diminishing with the excitation number, we find a form of bistability, where highly excited quasicoherent states (QCSs) coexist with the blockaded dim states (Fig. 1). In order to make use of this bistability to read out the qubit, it is necessary to solve the coherent control problem of selective population transfer, which is how to steer the system toward either the dim state or the QCS, depending on the initial state of the qubit (Fig. 2). This selective dynamical mapping of the qubit state to the dim or bright states constitutes the readout scheme. It is potentially of high contrast and hence robust against external amplifier imperfections. An advantage of this readout is that it uses no additional components beyond the qubit and the cavity, the latter already present as part of...
. J. Chem. 66, 2595Chem. 66, (1988.Laser flash photolysis studies lead to the conclusion that the short-lived triplet states of cyclohexenones are readily quenched by amines. For example, in the case of 2-cyclohexen-1-one (I) its triplet state (TT = 40 ns in acetonitrile) is quenched by triethylamine with a rate constant of (9.0 2 0.8) x lo7 M-' s-I. Cyclohexenone triplets are also quenched efficiently by DABCO and by triphenylamine leading to the formation of the corresponding amine radical cations. The new evidence reported rules out the involvement of long-lived detectable exciplexes. Cohen and Peters and their co-workers have studied this process with benzophenone and related ketones, and have demonstrated convincingly that the quenching process involves electron transfer to give initially amine radical cations and ketone radical anions (2). Schuster and Brisimitzakis demonstrated that reactive 2,5-cyclohexadienone triplets are quenched by amines of appropriate ionization potential to give a set of products not observed in the absence of amines. In all cases, the amine interacts directly with ketone triplet (3).Reactions of photoexcited a,~-unsaturated carbonyl compounds with amines are known to give 1:l adducts, presumably via the enone triplet states (4). Dunn et al. have reported results of nanosecond flash studies on excitation of cvclohexanone I and analogues such as I1 (see Chart I) in the presence of 1,4-diazabicyclo [2.2.2]octane (DABCO) which demonstrate that long-lived DABCO radical cations (X,,, 450 nm) are formed from an intermediate which has the same lifetime (ca. 25 ns) as the transient species (X,,, 280 nm) generated on laser excitation of the enone in the absence of amines (5). This transient has been suggested by Bonneau (6) and by Schuster et al. (7) to be a highly twisted triplet excited state of these cyclohexenones. In the presence of even small amounts of DABCO, long-lived absorption is observed which interferes with analysis of the fast component of the decay curve at wavelengths in the range 270-300 nm; at the DABCO concentrations required for observation of the growth of the radical cation at 450 nm, the fast decay at 280 nm cannot be monitored (5,8).In contrast to the above findings, Pienta and McKimmey reported results of product analyses from excitation of I in the
Das Butanon (II), dessen direkte Photolyse das Methylketon (I) liefert, und das bei Aceton‐sensibilisierter Anregung außerdem das bicyclische Keton (III) als Produkt einer 1,2‐sigmatropen Acetylverschiebung bildet, zeigt bei einer Photoreaktion unter 2.2 at Xe eine Abnahme der Intensität der Fluoreszenz von (II) um 21% bei gleichzei‐ tiger Steigerung der Quantenausb.
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