Entanglement between two superconducting qubits via interaction with nonclassical radiation (original) (raw)
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Entangled Macroscopic Quantum States in Two Superconducting Qubits
Science, 2003
We present spectroscopic evidence for the creation of entangled macroscopic quantum states in two current-biased Josephson-junction qubits coupled by a capacitor. The individual junction bias currents are used to control the interaction between the qubits by tuning the energy level spacings of the junctions in and out of resonance with each other. Microwave spectroscopy in the 4 to 6 gigahertzrange at 20 millikelvin reveals energy levels that agree well with theoretical results for entangled states. The single qubits are spatially separate, and the entangled states extend over the 0.7-millimeter distance between the two qubits.
Entanglement of superconducting qubits via microwave fields: Classical and quantum regimes
Physical Review B, 2008
We study analytically and numerically the problem of two qubits with fixed coupling irradiated with quantum or classical fields. In the classical case, we derive an effective Hamiltonian and describe its entangling properties. We identify a coupling/decoupling switching protocol and we construct composite pulse sequences leading to a CNOT gate. In the quantum case, we show that qubit-qubit-photon multiparticle entanglement and maximally entangled two-qubit states can be obtained by driving the system at very low powers (one quanta of excitation). Our results can be applied to a variety of systems of two superconducting qubits coupled to resonators.
Quantum State Transmission in a Superconducting Charge Qubit-Atom Hybrid
Scientific reports, 2016
Hybrids consisting of macroscopic superconducting circuits and microscopic components, such as atoms and spins, have the potential of transmitting an arbitrary state between different quantum species, leading to the prospective of high-speed operation and long-time storage of quantum information. Here we propose a novel hybrid structure, where a neutral-atom qubit directly interfaces with a superconducting charge qubit, to implement the qubit-state transmission. The highly-excited Rydberg atom located inside the gate capacitor strongly affects the behavior of Cooper pairs in the box while the atom in the ground state hardly interferes with the superconducting device. In addition, the DC Stark shift of the atomic states significantly depends on the charge-qubit states. By means of the standard spectroscopic techniques and sweeping the gate voltage bias, we show how to transfer an arbitrary quantum state from the superconducting device to the atom and vice versa.
Physical review letters, 2018
Large-scale quantum information processing networks will most probably require the entanglement of distant systems that do not interact directly. This can be done by performing entangling gates between standing information carriers, used as memories or local computational resources, and flying ones, acting as quantum buses. We report the deterministic entanglement of two remote transmon qubits by Raman stimulated emission and absorption of a traveling photon wave packet. We achieve a Bell state fidelity of 73%, well explained by losses in the transmission line and decoherence of each qubit.
Quantum deficits and correlations of two superconducting charge qubits
Physica C: Superconductivity, 2009
Motivated by recent experiments [Pashkin et al. Nature, 421, 823 (2003)] which showed coherent oscillations of two superconducting qubits system, we consider a system of two charge qubits coupled to a common stripline microwave resonator. We discuss the separable and entangled behavior as well as the quantum and classical information deficits. Numerical computation of these quantities for several regimes is performed. We find that for less entangled states the partner can extract much more information by means of classical communication and local operations.
Quantum information processing with superconducting qubits in a microwave field
Physical Review B, 2003
We investigate the quantum dynamics of a Cooper-pair box with a superconducting loop in the presence of a nonclassical microwave field. We demonstrate the existence of Rabi oscillations for both single-and multi-photon processes and, moreover, we propose a new quantum computing scheme (including one-bit and conditional two-bit gates) based on Josephson qubits coupled through microwaves.
Generating entanglement via measurement between two remote superconducting qubits
Bulletin of the American Physical Society, 2014
Measurement has traditionally been viewed as a means to restore classical behavior to a quantum system: a coherent superposition, once observed, transforms into a single classical state. However, it is possible to design a measurement that instead projects into an entangled state, thereby purifying, rather than destroying, quantum correlations. We use continuous measurement to generate entanglement between two superconducting qubits that are separated by more than a meter of cable, demonstrating that quantum information can be transferred over the metallic wires that comprise a low-loss channel for microwave photon propagation. We further generate a faithful, time-resolved record of single quantum trajectories. Studying the statistics of these trajectories and of the ensemble of measurements provides insight into the dynamics of measurement-induced entanglement in an extended quantum network.
Time evolution and decoherence of entangled states realized in coupled superconducting flux qubits
We study theoretically how decoherence affects superposition states composed of entangled states in inductively coupled two superconducting flux-qubits. We discover that the quantum fluctuation of an observable in a coupled flux-qubit system plays a crucial role in decoherence when the expectation value of the observable is zero. This examplifies that decoherence can be also induced through a quantum mechanically higher-order effect. We also find that there exists a decoherence free subspace for the environment coupled via a charge degree of freedom of the qubit system.
Physical Review Letters, 2012
We report a system where fixed interactions between non-computational levels make bright the otherwise forbidden two-photon |00 → |11 transition. The system is formed by hand selection and assembly of two discrete component transmon-style superconducting qubits inside a rectangular microwave cavity. The application of a monochromatic drive tuned to this transition induces twophoton Rabi-like oscillations between the ground and doubly-excited states via the Bell basis. The system therefore allows all-microwave two-qubit universal control with the same techniques and hardware required for single qubit control. We report Ramsey-like and spin echo sequences with the generated Bell states, and measure a two-qubit gate fidelity of Fg = 90% (unconstrained) and 86% (maximum likelihood estimator).