Josephson Junctions: Finding the Magnetic Flux Quantum

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Josephson Junctions Finding the Magnetic Flux
Quantum

• Chintan Hossain

MIT Junior Lab May 12, 2005
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Outline

• Background Superconductivity, Josephson
  Junctions
• Experimental Setup
• Data and Results Magnetic flux quantum
• Conclusion

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Superconductivity

• Electrons form Cooper pairs at low temperatures
  due to attractive forces
• Cooper pairs are Bosons all condense into the
  same state
• Wavefunction of Cooper pairs is

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Josephson Junction

• Two superconductors separated by a small
  insulating gap
• Current flows across the gap due to tunneling of
  Cooper pairs.
• Shows quantum mechanical properties on a
  macroscopic scale.

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Wavefunction in a Josephson Junction
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Current vs. Voltage
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Current vs. Magnetic Field
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Experimental Apparatus
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Solenoid Calibration
Data from Vjekoslav Svilan
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Current vs. Magnetic Field
Data from Vjekoslav Svilan
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Final Results

• F0/A02.29 0.05 Gauss
• F01.28 x 10-15 0.03 Tm2
• Known value 2.07 x 10-15 Tm2
• Our value is off by a factor of 0.62

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Possible Problems

• Wrong values of ?1 and ?2 used values increase
  with temperature
• Improper calibration Magnetic field may have
  been measured outside solenoid

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Sources of Error

• Calibration error (Field vs. Solenoid current
  fit) 1.8
• Josephson Current vs. Field fit 1.0

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Conclusion

• We obtained a value for the magnetic flux
  quantum F01.28 x 10-15 0.03 Tm2
• Actual value 2.07 x 10-15 Tm2
• Our value is off by 0.62
• Possible reasons for disagreement
• Wrong values of ?1 and ?2
• Improper calibration