High-Efficiency Measurement of an Artificial Atom Embedded in a Parametric Amplifier

Abstract

A crucial limit to measurement efficiencies of superconducting circuits comes from losses involved when coupling to an external quantum amplifier. Here, we realize a device circumventing this problem by directly embedding a two-level artificial atom, comprised of a transmon qubit, within a flux-pumped Josephson parametric amplifier. Surprisingly, this configuration is able to enhance dispersive measurement without exposing the qubit to appreciable excess backaction. This is accomplished by engineering the circuit to permit high-power operation that reduces information loss to unmonitored channels associated with the amplification and squeezing of quantum noise. By mitigating the effects of off-chip losses downstream, the on-chip gain of this device produces end-toend measurement efficiencies of up to 80%. Our theoretical model accurately describes the observed interplay of gain and measurement backaction, and delineates the parameter space for future improvement. The device is compatible with standard fabrication and measurement techniques, and thus provides a route for definitive investigations of fundamental quantum effects and quantum control protocols. arXiv:1806.05276v1 [quant-ph]

Non-Hermitian dynamics without dissipation in quantum systems

“…In this case, the matrix Ω becomes an overall constant in the non-Hermtian Hamil-tonianĤ tb and can be ignored, and our mapping shows that the dynamics is equivalent to a simple two-mode NDPA in Eq. (38). We stress that this is a distinct mapping from that in Sec.…”

“…Note that the perturbation is now a standard dispersive coupling, something that arises in many measurement contexts. In the case where corresponds to the state of a qubit, this exact setup was realized in a recent superconducting quantum circuit experiment (though operated in a different regime) [38].…”

Tomography of an optomechanical oscillator via parametrically amplified position measurement

“…Furthermore, in [43][44][45] it is shown that, in conjunction with continuous measurement, arbitrarily high levels of squeezing can be achieved in principle. This proposal is closely analogous to a recent experiment in circuit QED has used parametric drive of a microwave cavity to improve the effective efficiency of measurements on transmon qubits [46]. Importantly for quantum state tomography, parametric amplification adds no noise, in principle, and is therefore very effective at transducing small signals.…”

Symmetries and physically realisable ensembles for open quantum systems

“…The parameter choice is γ + =0.05γ − . 10 A straightforward way to verify this is to formulate the constraint equations in terms of the Bloch vectors (rather than the state vectors of equation (4)) then, due to the symmetry of the system, choose say v 1 =0. By inspection, this will lead to v 2 =v 3 =0 also.…”

“…Questions of this type [1] may offer novel insights into the nature of open quantum system dynamics and the quantum-classical epistemic distinction [2][3][4]. The observation of single quantum trajectories has now been realised in the laboratory [5][6][7][8][9], with ever increasing detection efficiencies [10]. Additionally, there is strong theoretical evidence for the stability of the particular class of quantum trajectories under consideration [11].…”