An Interview with Professor Siddiqi: Quantum Scale Measurements

How did you get started in your field of research?Dr. Siddiqi: I am working now with quantum information devices, putting together quantum mechanics with electronics.Of course I didn't do that when I was an undergrad.In reality, science is motivated by fundamental questions, and the overarching theme that links all of this is how to use superconductive devices.These are devices that don't have resistance.In the early days of this science, these devices were used as amplifiers.They still are, of course, for detectors and for astronomy.This is because you get rid of resistors, which are a source of noise.This is classical noise due to thermal fluctuations.If you get rid of this noise, things get very quiet and you have very good detectors.Later on, it was realized that if you get rid of this resistor then you can also have things that have a long life time in the quantum mechanical sense.In an amplifier, you don't make an oscillator, or a pendulum, you make something with no Q (the quality factor, or the Q factor).If you were to make an amplifier or a pendulum, without a resistor it just keeps on ringing.This isn't always the most useful device in the classical domain, but in the quantum domain it is very useful.What this means is if you have a system with quantized energy levels, the life time is very long.For example, let's translate from the classical world to the quantum world.I take a pendulum, a mass on a spring.It oscillates by going back and forth like a sine wave.The quantum version of this is that you have a system with multiple levels and it goes back and forth between levels.This is called Rabi oscillations, the quantum analog to a pendulum.Those oscillations also die out over a period of time, depending on how much resistance you have.In the classical sense, you would have drag that slows the pendulum down, in the quantum sense, you can have noise that slows that delay down.So if you want to keep quantum systems alive, it's the same in the classical sense as having an oscillator which doesn't break down or has a high Q.So a lot of the science that we learned in the old days of low temperature physics with superconductors and electronics has mapped onto the quantum problem.We simply quantized a lot of those techniques we knew from the classical domain.At the same time, we discovered that you can actually use these quantum devices for something, for information processing, for factoring numbers and cryptography, for simulation, for information and so on.BSJ: We were also interested in your personal attachment to the research, and how you picked quantum information