1,527 research outputs found
Cavity-QED based on collective magnetic dipole coupling: spin ensembles as hybrid two-level systems
We analyze the magnetic dipole coupling of an ensemble of spins to a
superconducting microwave stripline structure, incorporating a Josephson
junction based transmon qubit. We show that this system is described by an
embedded Jaynes-Cummings model: in the strong coupling regime, collective
spin-wave excitations of the ensemble of electrons pick up the nonlinearity of
the cavity mode, such that the two lowest eigenstates of the coupled spin-wave
+ microwave-cavity + Josephson-junction system define a hybrid two-level
system. The proposal described here enables the use of spin ensembles as qubits
which can be coherently manipulated and coupled using the same
nonlinear-cavity. Possibility of strong-coupling cavity-QED with
magnetic-dipole transitions opens up the possibility of extending previously
proposed quantum information processing protocols to spins in silicon or
graphene, without the need for single-electron confinement.Comment: 4 page
Ultra-long distance interaction between spin qubits
We describe a method for implementing deterministic quantum gates between two
spin qubits separated by centimeters. Qubits defined by the singlet and triplet
states of two exchange coupled quantum dots have recently been shown to possess
long coherence times. When the effective nuclear fields in the two asymmetric
quantum dots are different, total spin will no longer be a good quantum number
and there will be a large electric dipole coupling between the two qubit
states. We show that when such a double-quantum-dot qubit is embedded in a
superconducting microstrip cavity, the strong coupling regime of cavity quantum
electrodynamics lies within reach. Virtual photons in a common cavity mode
could mediate coherent interactions between two distant qubits embedded in the
same structure; the range of this two-qubit interaction is determined by the
wavelength of the microwave transition.Comment: 5 pages, 2 figures; final version v2 (minor changes
Recommended from our members
Photoactivated biological processes as quantum measurements.
We outline a framework for describing photoactivated biological reactions as generalized quantum measurements of external fields, for which the biological system takes on the role of a quantum meter. By using general arguments regarding the Hamiltonian that describes the measurement interaction, we identify the cases where it is essential for a complex chemical or biological system to exhibit nonequilibrium quantum coherent dynamics in order to achieve the requisite functionality. We illustrate the analysis by considering measurement of the solar radiation field in photosynthesis and measurement of the earth's magnetic field in avian magnetoreception
- …