Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Oxford University Press eBooks

Taming Schrödinger’s cat

S. Haroche, J. M. Raimond

Published Aug 10, 2006• 0 citations
Publisher

Abstract

This chapter is devoted to the physics of cavity quantum electrodynamics (CQED) cats. After a brief reminder about the Schrödinger cat problem in quantum optics, it describes how a single atom interacting with a field made of many photons can leave its quantum imprint on this field, bringing it into a superposition of states with distinct classical attributes. It describes the preparation and detection of these ‘Schrödinger cat’ states. It presents simple decoherence models, which account for their extreme fragility. It describes experimental studies of decoherence, which constitute direct explorations of the quantum-classical boundary. It discusses limitations to the size of these cat states and ways to protect them efficiently against decoherence. Finally, the chapter describes proposals to generate and study non-local cats, superpositions of field states delocalised in two cavities.

DOI
10.1093/acprof:oso/9780198509141.003.0007

Related papers

Quantum superpositions and Schrödinger cat states in quantum optics

Christopher C. Gerry, P. L. Knight

We describe the properties of a quantum system prepared in superpositions of classically distinguishable states. These states, often called Schrödinger cat states, are of great interest at present. We discuss how they may be realized in quantum optics using nonlinear interactions and cavity quantum electrodynamics. We first describe the quantum properties of field states in a cavity, and demonstrate the interference properties which characterize superposition states and discuss how fragile they are in dissipative environments. Finally, we review current experimental approaches which may realize these states.

American Journal of Physics•Oct 1, 1997•152 citations

Photons in a box and 'Schrödinger Cats' of light

S. Haroche

The founders of quantum physics used to analyse thought experiments, to discuss state superposition, complementarity and entanglement. They imagined manipulating single particles, such as electrons, atoms or photons; they would be surprised to see that experiments with isolated atoms, molecules or photons are now carried on in many laboratories throughout the world. In our Cavity Quantum Electrodynamics (CQED) studies, we stabilize and count photon number states in the cavity. We also prepare and reconstruct photonic superposition states suspended between different 'classical realities', generating a laboratory version of Schrodinger famous 'Cat', which he had imagined to be simultaneously dead and alive. We have also investigated the decoherence process, which explains the transition between the quantum and the classical worlds. CQED physics has recently been extended to artificial 'atoms' made from superconductors, in a new domain of mesoscopic physics called Circuit QED. This development opens the way to applications in quantum information science.

•Jan 1, 2015•0 citations

Quantum information in cavity quantum electrodynamics: logical gates, entanglement engineering and ‘Schrödinger–cat states’

S. Haroche

In cavity-quantum-electrodynamics experiments, two-level Rydberg atoms and single-photon microwave fields can be seen as qubits. Quantum gates based on resonant and dispersive atom-field effects have been realized, which implement various kinds of conditional dynamics between these qubits. We have also studied the interaction between a single atom and coherent fields stored in the cavity. By progressively increasing the number of photons in these fields, we have explored various aspects of the quantum-classical boundary. We have realized a complementarity experiment demonstrating the continuous evolution of an apparatus from a quantum to a classical behaviour. We have also prepared 'Schrödinger-cat'-like states of the field made of a few photons, and observed their decoherence. We present a brief review of these experiments along with a proposal to study larger systems, i.e. coherent fields with more photons. Fundamental limits to the size of mesoscopic superpositions of field states in a cavity will be briefly discussed.

Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences•Jul 15, 2003•37 citations

Colloquium: Manipulating quantum entanglement with atoms and photons in a cavity

J. M. Raimond, M. Brune, S. Haroche

After they have interacted, quantum particles generally behave as a single nonseparable entangled system. The concept of entanglement plays an essential role in quantum physics. We have performed entanglement experiments with Rydberg atoms and microwave photons in a cavity and tested quantum mechanics in situations of increasing complexity. Entanglement resulted either from a resonant exchange of energy between atoms and the cavity field or from dispersive energy shifts affecting atoms and photons when they were not resonant. With two entangled particles (two atoms or one atom and a photon), we have realized new versions of the Einstein-Podolsky-Rosen situation. The detection of one particle projected the other, at a distance, in a correlated state. This process could be viewed as an elementary measurement, one particle being a ‘‘meter’’ measuring the other. We have performed a ‘‘quantum nondemolition’’ measurement of a single photon, which we detected repeatedly without destroying it. Entanglement is also essential to understand decoherence, the process accounting for the classical appearance of the macroscopic world. A mesoscopic superposition of states (‘‘Schrodinger cat’’) gets rapidly entangled with its environment, losing its quantum coherence. We have prepared a Schrodinger cat made of a few photons and studied the dynamics of its decoherence, in an experiment which constitutes a glimpse at the quantum/classical boundary. We have also investigated entanglement as a resource for the processing of quantum information. By using quantum two-state systems (qubits) instead of classical bits of information, one can perform logical operations exploiting quantum interferences and taking advantage of the properties of entanglement. Manipulating as qubits atoms and photons in a cavity, we have operated a quantum gate and applied it to the generation of a complex three-particle entangled state. We finally discuss the perspectives opened by these experiments for further fundamental studies.

•Jan 1, 2001•90 citations

Experiments with single atoms in a cabity: entanglement, Schrödinger's cats and decoherence

S. Haroche, M. Brune, J. M. Raimond

We perform experiments with Rydberg atoms crossing one at a time a superconducting cavity containing a few microwave photons. The coupling between the atoms and the cavity field is either resonant or dispersive. In the resonant case, quantum Rabi oscillations induced by the vacuum or by a small coherent field are observed. These signals reveals in a striking way the quantization of the field. Quantum Rabi oscillations are also used to prepare Fock states of radiation, to transfer information or to produce entanglement between two successive atoms crossing the cavity. Dispersive atom–field coupling is used to prepare and probe coherent superpositions of field states with different phases (Schrödinger's cat states). The progressive decoherence of these states is observed. These experiments constitute fundamental tests of quantum theory and shed light on the transition from quantum to classical in mesoscopic systems.

Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences•Dec 15, 1997•44 citations

An experimental study of a schrödinger cat decoherence with atoms and cavities

X. Ma[icaron]tre, E. W. Hagley, J. Dreyer +5 more

The dynamics of quantum decoherence have been experimentally studied for the first time. A single circular Rydberg atom prepares in a high-quality superconducting cavity a ‚Schrödinger cat‘ state of the radiation field. This highly non-classical state is a quantum superposition of two coherent components with different classical phases. A second atom probes the cavity state after a tunable delay. The decay of the quantum correlations between the two atoms reveals the evolution of the initial quantum superposition into a mere statistical mixture. The time scale of this process decreases when the separation beween the two components increases. A simple theoretical model of the experiment is presented. The excellent agreement with the experimental signals confirms in a striking way the decoherence approach.

Journal of Modern Optics•Nov 1, 1997•10 citations
This chapter is devoted to the physics of cavity quantum electrodynamics (CQED) cats. After a brief reminder about the Schrödinger cat problem in quantum optics, it describes how a single atom interacting with a field made of many photons can leave its quantum imprint on this field, bringing it into a superposition of states with distinct classical attributes. It describes the preparation and detection of these ‘Schrödinger cat’ states. It presents simple decoherence models, which account for their extreme fragility. It describes experimental studies of decoherence, which constitute direct explorations of the quantum-classical boundary. It discusses limitations to the size of these cat states and ways to protect them efficiently against decoherence. Finally, the chapter describes proposals to generate and study non-local cats, superpositions of field states delocalised in two cavities.
We describe the properties of a quantum system prepared in superpositions of classically distinguishable states. These states, often called Schrödinger cat states, are of great interest at present. We discuss how they may be realized in quantum optics using nonlinear interactions and cavity quantum electrodynamics. We first describe the quantum properties of field states in a cavity, and demonstrate the interference properties which characterize superposition states and discuss how fragile they are in dissipative environments. Finally, we review current experimental approaches which may realize these states.
The founders of quantum physics used to analyse thought experiments, to discuss state superposition, complementarity and entanglement. They imagined manipulating single particles, such as electrons, atoms or photons; they would be surprised to see that experiments with isolated atoms, molecules or photons are now carried on in many laboratories throughout the world. In our Cavity Quantum Electrodynamics (CQED) studies, we stabilize and count photon number states in the cavity. We also prepare and reconstruct photonic superposition states suspended between different 'classical realities', generating a laboratory version of Schrodinger famous 'Cat', which he had imagined to be simultaneously dead and alive. We have also investigated the decoherence process, which explains the transition between the quantum and the classical worlds. CQED physics has recently been extended to artificial 'atoms' made from superconductors, in a new domain of mesoscopic physics called Circuit QED. This development opens the way to applications in quantum information science.
In cavity-quantum-electrodynamics experiments, two-level Rydberg atoms and single-photon microwave fields can be seen as qubits. Quantum gates based on resonant and dispersive atom-field effects have been realized, which implement various kinds of conditional dynamics between these qubits. We have also studied the interaction between a single atom and coherent fields stored in the cavity. By progressively increasing the number of photons in these fields, we have explored various aspects of the quantum-classical boundary. We have realized a complementarity experiment demonstrating the continuous evolution of an apparatus from a quantum to a classical behaviour. We have also prepared 'Schrödinger-cat'-like states of the field made of a few photons, and observed their decoherence. We present a brief review of these experiments along with a proposal to study larger systems, i.e. coherent fields with more photons. Fundamental limits to the size of mesoscopic superpositions of field states in a cavity will be briefly discussed.
After they have interacted, quantum particles generally behave as a single nonseparable entangled system. The concept of entanglement plays an essential role in quantum physics. We have performed entanglement experiments with Rydberg atoms and microwave photons in a cavity and tested quantum mechanics in situations of increasing complexity. Entanglement resulted either from a resonant exchange of energy between atoms and the cavity field or from dispersive energy shifts affecting atoms and photons when they were not resonant. With two entangled particles (two atoms or one atom and a photon), we have realized new versions of the Einstein-Podolsky-Rosen situation. The detection of one particle projected the other, at a distance, in a correlated state. This process could be viewed as an elementary measurement, one particle being a ‘‘meter’’ measuring the other. We have performed a ‘‘quantum nondemolition’’ measurement of a single photon, which we detected repeatedly without destroying it. Entanglement is also essential to understand decoherence, the process accounting for the classical appearance of the macroscopic world. A mesoscopic superposition of states (‘‘Schrodinger cat’’) gets rapidly entangled with its environment, losing its quantum coherence. We have prepared a Schrodinger cat made of a few photons and studied the dynamics of its decoherence, in an experiment which constitutes a glimpse at the quantum/classical boundary. We have also investigated entanglement as a resource for the processing of quantum information. By using quantum two-state systems (qubits) instead of classical bits of information, one can perform logical operations exploiting quantum interferences and taking advantage of the properties of entanglement. Manipulating as qubits atoms and photons in a cavity, we have operated a quantum gate and applied it to the generation of a complex three-particle entangled state. We finally discuss the perspectives opened by these experiments for further fundamental studies.
We perform experiments with Rydberg atoms crossing one at a time a superconducting cavity containing a few microwave photons. The coupling between the atoms and the cavity field is either resonant or dispersive. In the resonant case, quantum Rabi oscillations induced by the vacuum or by a small coherent field are observed. These signals reveals in a striking way the quantization of the field. Quantum Rabi oscillations are also used to prepare Fock states of radiation, to transfer information or to produce entanglement between two successive atoms crossing the cavity. Dispersive atom–field coupling is used to prepare and probe coherent superpositions of field states with different phases (Schrödinger's cat states). The progressive decoherence of these states is observed. These experiments constitute fundamental tests of quantum theory and shed light on the transition from quantum to classical in mesoscopic systems.
The dynamics of quantum decoherence have been experimentally studied for the first time. A single circular Rydberg atom prepares in a high-quality superconducting cavity a ‚Schrödinger cat‘ state of the radiation field. This highly non-classical state is a quantum superposition of two coherent components with different classical phases. A second atom probes the cavity state after a tunable delay. The decay of the quantum correlations between the two atoms reveals the evolution of the initial quantum superposition into a mere statistical mixture. The time scale of this process decreases when the separation beween the two components increases. A simple theoretical model of the experiment is presented. The excellent agreement with the experimental signals confirms in a striking way the decoherence approach.