Enhanced qubit readout using locally generated squeezing and inbuilt Purcell-decay suppression

Abstract

We introduce and analyze a dispersive qubit readout scheme where two-mode squeezing is generated directly in the measurement cavities. The resulting suppression of noise enables fast, high-fidelity readout of naturally weakly coupled qubits, and the possibility to protect strongly coupled qubits from decoherence by weakening their coupling. Unlike other approaches exploiting squeezing, our setup avoids the difficult task of transporting and injecting with high fidelity an externally generated squeezed state. Our setup is also surprisingly robust against unwanted non-QND backaction effects, as interference naturally suppresses Purcell decay: the system acts as its own Purcell filter. Our setup is compatible with the experimental state-of-the-art in circuit QED systems, but the basic idea could also be realized in other systems.

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

“…In contrast, the noise fluctuations do get amplified (squeezed), such that the SNR at the QPA output depends on Φ. Since amplifying the signal quadrature squeezes the photon number fluctuations in the conjugate quadrature which cause dephasing, we expect amplifier mode (Φ = 0) to minimize Γ φ and squeezer mode (Φ = π/2) to maximize it, in agreement with the comparison of Figs We note that squeezer mode is also of interest as a means of improving SNR by reducing the quantum fluctuations of the output measurement field [24,31,32]; similar insitu squeezing generation has been demonstrated in a recent optical experiment [33].…”

Magnetic Resonance with Squeezed Microwaves

“…This triggered the development of practical Josephson parametric amplifier (JPA) devices [16][17][18][19] and follow-up amplifier chains such that the output noise is dominated by quantum fluctuations [20]. Microwave squeezed states [20] can then provide a sizable noise reduction, thus improving measurement sensitivity for qubit state readout [21][22][23][24] and nanomechanical resonator motion detection [25]. They have also been investigated for their effect on the dynamics of quantum systems, such as two-level atoms [26][27][28] or mechanical oscillators [29].…”

Exotic Quantum States of Circuit Quantum Electrodynamics in the Ultra‐Strong Coupling Regime

“…Such QND measurements have played crucial roles for the development of the quantum information processors based on circuit QED. [2,[37][38][39][40][41][42][43][44]…”