Summer Science Exhibition 2011

5-10 July | Free entry

The Royal Society

  • Quantum computing

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    Schrödinger’s cat in a silicon chip

    Schrödinger’s Frog. The picture shows the rows of individual atoms at the surface of a silicon crystal, imaged with the best microscope in existence, the scanning tunnelling microscope. Bulging out of the surface is a single foreign atom deliberately introduced to act as the world’s smallest circuit component, the quantum bit. The legs of the “frog” are distorted neighbouring silicon atoms, pushed out of shape by the much larger inclusion.

    Wave-particle duality is the principle in quantum physics that very small objects like electrons can sometimes behave like particles and sometimes behave like waves.  When we observe waves we see effects that we don’t normally associate with moving objects, such as interference and superposition of different frequencies (like when you play an octave chord).

    The exhibit explains how scientists have made electrons in a silicon chip behave like waves in just these kinds of ways – destructively cancelling each other out and chiming in chords. Visitors can learn how scientists are making use of some of this quantum wave-particle weirdness to develop a new kind of powerful computer.  

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    How does it work?

    Silicon, next to iron, is the most important crystalline solid in modern technology. It can be produced with astonishing purity in crystals of near perfect regularity.  Silicon computer chips are produced by taking a high purity crystal and then replacing a small percentage of the silicon with different atoms like phosphorus or boron, in carefully controlled patterns.

    The scientists behind this exhibit took some standard silicon with phosphorus atoms, and used light beams to make the electrons orbiting the phosphorus perform a synchronised dance, each atom both dancing and not dancing at the same time. This is an example of the situation of Schrodinger’s famous cat, which was at once both alive and dead.,However, this experiment had a wonderful new twist, since the scientists could controlhow much “alive” and how much “dead” using the light beams (from a laser coincidentally called Felix).  The scientists are also developing the capability to position individual phosphorus atoms precisely where they want to - so they can connect the dancers together, and build a “quantum computer”. For further information about thi sproject please see Compasss.

    What would you do if you could be in two places at once?

    Over the course of the Summer Science Exhibition, visitors to the stand were asked what they would do if they were in two places at once.  The best suggestion of the week won a guitar. 

    The shortlist included:
    "I would be in the crowd at a music festival while hang-gliding above it"
    "Climbing Everest and organising the rescue!"
    "I would do cartwheels + build robots at the same time"
    "Play princesses + robots at the same time."
    "I would tickle myself .... hehe"
    "KICK the second guitarist out of the band and do all the duties myself"
    "Go through two Young's Slits"
    "Give myself a high 5 across the border of 2 neighbouring countries"
    "Travel around the world in opposite directions + meet myself in the middle, having travelled around the whole world already!"

    The winning entry is "Tell my other self a joke to see if I'm funny".

     

    Videos

    This video illustrates some of the science demonstrated by this exhibit.

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