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Information quantique avec des atomes et des cavités.
Trois points pour ’tricoter’ un état intriqué
The resonant quantum Rabi oscillation is at the heart of quantum information processing with atoms and cavities. Selected interaction times provide the basic stitches that create and process atom-field entanglement. The stitches can be knitted in more complex sequences for the generation of multi-qubit entangled states.
This figure presents the first period of the quantum Rabi oscillation signal. Let us recall that the atom enters the empty cavity in the upper state $e$. The probability (...)
Une mémoire quantique
We demonstrate the coherent quantum information transfer from an atom to the cavity and back to a second atom. The cavity is here a quantum memory, storing a qubit for a time in the second range. The write and read operations involve flying atomic qubits.
This experiment is based on the $\pi$ quantum Rabi pulse, perfoming a qubit-copy operation from atom to cavity or back. The state of a first atom is copied onto the initially empty cavity mode and stored in this mode for a while. It is (...)
Intrication de deux modes du champ
A single atom is used to entangle the two non-degenrate modes of a cavity. In the entangled state, a single photon is shared by the two modes. The coherence of this state is probed by another atom.
In this experiment , we let an atom interact coherently with the two non-degenerate modes $M_a$ and $M_b$ ($M_b$ has the lowest frequency) of the cavity with orthogonal linear polarizations. This experiment has been performed with an early generation of cavity. The modes lifetime is of the order (...)
Génération d’une paire EPR atomique
We create an entangled atomic pair of the EPR type. The two atoms never interact directly. The entanglement is mediated by their successive interactions with the cavity mode.
The experiment uses two atoms crossing the cavity successively. The first, $A_1$, is prepared in $e$ and interacts with the cavity for a $\pi/2$ quantum Rabi pulse, creating the atom-cavity entangled state $ ; e,0\rangle+ ; g,1\rangle$ (we omit trivial normalizations).
This atom-cavity entanglement cannot be directly (...)
Une porte quantique atome/cavité
The quantum Rabi oscillation, for a full period of the coherent atom-cavity energy exchange, realizes a quantum phase gate, which can be easily turned into a CNOT gate by means of additional Ramsey pulses. Ths gate can in principle be used to prepare complex entangled states. It also leads to a quantum non demolition measurement of a single photon.
The EPR pair generation procedure, using the cavity as an entanglement catalyst, is obviously limited to two atoms. To knit more complex (...)
Génération pas à pas d’un état intriqué à trois qubits.
Using the phase gate, we prepare an entangled state of three qubits (two atoms and the cavity mode). This is a rather complex quantum information procedure, involving up to three one-qubit and three two-qubit quantum gates.
This experiment makes use of three qubits, two atoms, $A_1$ and $A_2$, and the cavity field $C$. A third atomic qubit, $A_3$, is used later for the cavity-state readout.
Preparation of the entangled state
The atom $A_1$ is prepared in $e$ and crosses the initially (...)
Intrication par collision coherente dans la cavité
Quantum gates based on the resonant atom-field interaction are limited by the cavity losses. We present here a direct entanglement generation between two atoms. The atoms interact simultaneously with the detuned cavity mode. The mode enhances the van der Waals interaction between the atoms and results in a coherent cavity-mediated ’collision’ generating entanglement. The scheme is nearly insensitive to cavity losses.
Atom-atom entanglement in free space
Atom-atom entanglement can, in (...)
