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Updated: Jul 11, 2026

Setting Limits on Supersymmetry Using Simplified Models
07:46

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Published on: November 15, 2013

Entangled macroscopic quantum States in two superconducting qubits.

A J Berkley1, H Xu, R C Ramos

  • 1Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, MD 20742, USA. berkley@physics.umd.edu

Science (New York, N.Y.)
|May 17, 2003
PubMed
Summary

Researchers created entangled macroscopic quantum states in two Josephson-junction qubits. This demonstrates entanglement over a 0.7-millimeter distance, controlled by bias currents and confirmed by microwave spectroscopy.

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Area of Science:

  • Quantum physics
  • Superconducting circuits

Background:

  • Josephson-junction qubits are fundamental units in quantum computing.
  • Controlling interactions between qubits is crucial for creating entangled states.

Purpose of the Study:

  • To demonstrate the creation of entangled macroscopic quantum states in coupled Josephson-junction qubits.
  • To investigate the control of qubit interactions using bias currents.

Main Methods:

  • Utilized two current-biased Josephson-junction qubits coupled via a capacitor.
  • Employed microwave spectroscopy (4-6 GHz) at 20 millikelvin to probe energy levels.
  • Varied individual junction bias currents to control qubit interactions and resonance.

Main Results:

  • Spectroscopic evidence confirmed the creation of entangled macroscopic quantum states.
  • Observed energy levels closely matched theoretical predictions for entangled states.
  • Entangled states were sustained over a spatial separation of 0.7 millimeters between qubits.

Conclusions:

  • Successfully demonstrated entanglement in spatially separated macroscopic quantum systems.
  • Bias current control offers a viable method for tuning qubit interactions and achieving entanglement.
  • The findings support the scalability of superconducting qubits for quantum information processing.