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Viewpoint: Filling a cavity with photons, and watching them leave

Alexandre Blais, Jay Gambetta

Published Dec 8, 2008• 0 citations
OpenAlex

Abstract

Preparing a harmonic oscillator in a state with a well-defined energy is a tricky business. With the new tools provided by cavity and circuit quantum electrodynamics it is now possible to make these pure quantum states and watch how they evolve in time.

Related papers

Filling a cavity with photons, and watching them leave

Alexandre Blais, Jay Gambetta

Preparing a harmonic oscillator in a state with a well-defined energy is a tricky business. With the new tools provided by cavity and circuit quantum electrodynamics it is now possible to make these pure quantum states and watch how they evolve in time.

Physics•Dec 8, 2008•3 citations

Measurement and neural network-assisted control of quantum microwave modes with superconducting circuits

Hector Hutin

The association of a quantum bit and a harmonic mode dispersively coupled is one of the most studied systems in the field of quantum electrodynamics of superconducting circuits. It offers one of the most reliable current methods for measuring the state of a quantum bit in a non-destructive manner and has enabled numerous quantum information experiments, studying the information obtained through this measurement and the dynamics of the qubit when subjected to it. It also provides the ability to prepare and manipulate the quantum state of the harmonic mode via the qubit, allowing information to be stored and processed in this mode, which is fundamental to building a quantum processor. This thesis presents two experiments based on this architecture. The first demonstrates how to use qubit fluorescence to non-destructively read the number of photons contained in a microwave cavity in a single shot, that is, before the cavity has relaxed. This makes it possible to measure photon number trajectories and observe them leave the cavity one by one. The analysis of this experiment relies on a fluorescence analysis in terms of propagating modes and addresses a number of questions about the information that these modes may contain. The second is a demonstration of the use of a neural network for quantum state preparation in the cavity. Here, the goal is to accelerate the optimization of control electromagnetic pulses at the frequencies of the cavity and qubit to create a quantum state in the cavity with high fidelity, and this for a broad class of states. To evaluate the efficiency of this new optimization protocol over this class of states, an optimal method to assess the fidelity of the prepared states using a Wigner function measurement protocol was experimentally implemented for the first time.

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HERBERT WALTHER

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Quantum state engineering in finite-dimensional Hilbert space

Adam Miranowicz, W. Leoński, Sigurd Dyrting +1 more

We give a recipe for how to generate various harmonic oscillator states formally defined in finite-dimensional Hilbert space.

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Cloaking a qubit in a cavity

Cristóbal Lledó, Rémy Dassonneville, Adrien Moulinas +5 more

Cavity quantum electrodynamics (QED) uses a cavity to engineer the mode structure of the vacuum electromagnetic field such as to enhance the interaction between light and matter. Exploiting these ideas in solid-state systems has lead to circuit QED which has emerged as a valuable tool to explore the rich physics of quantum optics and as a platform for quantum computation. Here we introduce a simple approach to further engineer the light-matter interaction in a driven cavity by controllably decoupling a qubit from the cavity's photon population, effectively cloaking the qubit from the cavity. This is realized by driving the qubit with an external tone tailored to destructively interfere with the cavity field, leaving the qubit to interact with a cavity which appears to be in the vacuum state. Our experiment demonstrates how qubit cloaking can be exploited to cancel the ac-Stark shift and measurement-induced dephasing, and to accelerate qubit readout. In addition to qubit readout, applications of this method include qubit logical operations and the preparation of non-classical cavity states in circuit QED and other cavity-based setups.

arXiv:2211.05758•Nature Communications•Oct 9, 2023•21 citations

Scheme for steady-state preparation of a harmonic oscillator in the first excited state

Kjetil Børkje

We present a generic quantum master equation whose dissipative dynamics autonomously stabilizes a harmonic oscillator in the $n=1$ Fock state. A multimode optomechanical system is analyzed and shown to be an example of a physical system obeying this model. We show that the optomechanical setup enables preparation of a mechanical oscillator in a nonclassical steady state, and that this state indeed approaches a single phonon Fock state in the ideal parameter regime. The generic model may be useful in other settings, such as cavity or circuit quantum electrodynamics or trapped ion physics.

arXiv:1402.5057•Physical Review A•Aug 6, 2014•11 citations
The association of a quantum bit and a harmonic mode dispersively coupled is one of the most studied systems in the field of quantum electrodynamics of superconducting circuits. It offers one of the most reliable current methods for measuring the state of a quantum bit in a non-destructive manner and has enabled numerous quantum information experiments, studying the information obtained through this measurement and the dynamics of the qubit when subjected to it. It also provides the ability to prepare and manipulate the quantum state of the harmonic mode via the qubit, allowing information to be stored and processed in this mode, which is fundamental to building a quantum processor. This thesis presents two experiments based on this architecture. The first demonstrates how to use qubit fluorescence to non-destructively read the number of photons contained in a microwave cavity in a single shot, that is, before the cavity has relaxed. This makes it possible to measure photon number trajectories and observe them leave the cavity one by one. The analysis of this experiment relies on a fluorescence analysis in terms of propagating modes and addresses a number of questions about the information that these modes may contain. The second is a demonstration of the use of a neural network for quantum state preparation in the cavity. Here, the goal is to accelerate the optimization of control electromagnetic pulses at the frequencies of the cavity and qubit to create a quantum state in the cavity with high fidelity, and this for a broad class of states. To evaluate the efficiency of this new optimization protocol over this class of states, an optimal method to assess the fidelity of the prepared states using a Wigner function measurement protocol was experimentally implemented for the first time.
Cavity quantum electrodynamics (QED) uses a cavity to engineer the mode structure of the vacuum electromagnetic field such as to enhance the interaction between light and matter. Exploiting these ideas in solid-state systems has lead to circuit QED which has emerged as a valuable tool to explore the rich physics of quantum optics and as a platform for quantum computation. Here we introduce a simple approach to further engineer the light-matter interaction in a driven cavity by controllably decoupling a qubit from the cavity's photon population, effectively cloaking the qubit from the cavity. This is realized by driving the qubit with an external tone tailored to destructively interfere with the cavity field, leaving the qubit to interact with a cavity which appears to be in the vacuum state. Our experiment demonstrates how qubit cloaking can be exploited to cancel the ac-Stark shift and measurement-induced dephasing, and to accelerate qubit readout. In addition to qubit readout, applications of this method include qubit logical operations and the preparation of non-classical cavity states in circuit QED and other cavity-based setups.
We present a generic quantum master equation whose dissipative dynamics autonomously stabilizes a harmonic oscillator in the n=1n=1n=1 Fock state. A multimode optomechanical system is analyzed and shown to be an example of a physical system obeying this model. We show that the optomechanical setup enables preparation of a mechanical oscillator in a nonclassical steady state, and that this state indeed approaches a single phonon Fock state in the ideal parameter regime. The generic model may be useful in other settings, such as cavity or circuit quantum electrodynamics or trapped ion physics.