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arXiv:quant-ph/0105144

Spin squeezing of atoms by Rydberg blockade

Isabelle Bouchoule, Klaus Mølmer

Published May 29, 2001• 0 citations
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Abstract

We show that the interaction between Rydberg atomic states can provide continuous spin squeezing of atoms with two ground states. The interaction prevents the simultaneous excitation of more than a single atom in the sample to the Rydberg state, and we propose to utilize this blockade effect to realize an effective collective spin hamiltonian J_x^2-J_y^2. With this hamiltonian the quantum mechanical uncertainty of the spin variable J_x+J_y can be reduced significantly.

DOI
10.48550/arxiv.quant-ph/0105144

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We show that the interaction between Rydberg atomic states can provide continuous spin squeezing of atoms with two ground states. The interaction prevents the simultaneous excitation of more than a single atom in the sample to the Rydberg state, and we propose to utilize this blockade effect to realize an effective collective spin hamiltonian J_x^2-J_y^2. With this hamiltonian the quantum mechanical uncertainty of the spin variable J_x+J_y can be reduced significantly.
We show that the interaction between Rydberg atomic states can provide continuous spin squeezing of atoms with two ground states. The interaction prevents the simultaneous excitation of more than a single atom in the sample to the Rydberg state, and we propose to utilize this blockade effect to realize an effective collective spin Hamiltonian ${J}_{x}^{2}\ensuremath{-}{J}_{y}^{2}.$ With this Hamiltonian the quantum-mechanical uncertainty of the spin variable ${J}_{x}\ensuremath{-}{J}_{y}$ can be significantly reduced.
A scheme is proposed to prepare squeezed states and Schr\"odinger-cat-like states of the collective spin degrees of freedom associated with a pair of ground states in an atomic ensemble. The scheme uses an effective Jaynes-Cummings interaction which can be provided by excitation of the atoms to Rydberg states and an effective Jx{J}_{x}Jx​ interaction implemented by a resonant Raman coupling between the atomic ground states. Dynamical evolution both with a constant Hamiltonian and with adiabatic variation of the two interaction terms is studied. We show that by the application of further resonant laser fields, we can suppress nonadiabatic transfer under the time-varying Hamiltonian and significantly speed up the evolution towards a maximally squeezed, Jz=0{J}_{z}=0Jz​=0, collective spin state.
We propose to apply stimulated adiabatic passage to transfer atoms from their ground state into Rydberg excited states. Atoms a few micrometers apart experience a dipole-dipole interaction among Rydberg states that is strong enough to shift the atomic resonance and inhibit excitation of more than a single atom. We show that the adiabatic passage in the presence of this interaction between two atoms leads to robust creation of maximally entangled states and to two-bit quantum gates. For many atoms, the excitation blockade leads to an effective implementation of collective-spin and Jaynes-Cummings-like Hamiltonians, and we show that the adiabatic passage can be used to generate collective J_{x}=0 eigenstates and Greenberger-Horne-Zeilinger states of tens of atoms.
We propose a mechanism of ground-state blockade between two NNN-type Rydberg atoms by virtue of the Rydberg-antiblockade effect and the Raman transition. Inspired by the quantum Zeno effect, the strong Rydberg antiblockade interaction plays a role in frequently measuring one ground state of two, leading to a blockade effect for double occupation of the corresponding quantum state. By encoding the logic qubits into the ground states, we efficiently avoid the spontaneous emission of the excited Rydberg state and maintain the nonlinear Rydberg-Rydberg interaction at the same time. As applications, we discuss in detail the feasibility of preparing two-atom and three-atom entanglement with ground-state blockade in closed and open systems, respectively, which shows that a high fidelity of the entangled state can be obtained with current experimental parameters.
We report the generation of entanglement between two individual 87Rb atoms in hyperfine ground states |F=1,M=1> and |F=2,M=2> which are held in two optical tweezers separated by 4 microm. Our scheme relies on the Rydberg blockade effect which prevents the simultaneous excitation of the two atoms to a Rydberg state. The entangled state is generated in about 200 ns using pulsed two-photon excitation. We quantify the entanglement by applying global Raman rotations on both atoms. We measure that 61% of the initial pairs of atoms are still present at the end of the entangling sequence. These pairs are in the target entangled state with a fidelity of 0.75.
Atoms excited to high lying g quantum states, so-called Rydberg atoms, are highly polarizable and, therefore interact strongly with each other at large distances. One result of these interactions is the Rydberg dipole blockade effect, in which strongly interacting atoms excited by the same driving pulse may prevent other atoms from getting excited. This blockade offers several applications, for example the realization of quantum logic gates [1] and the possibility \nof creating entangled states with two atoms [2].