Quantum computing for ????????????????????? "uncles”

The challenge to explain Quantum Computing to my 13 years old niece made me approach to this with authentic enthusiasm. There are countless videos online, and tutorials on the topic, but according to many enthusiast viewers, it seems they give the feeling of having grasped a little bit of the concepts, but in reality, leaving more questions than answers.

Quantum Computing is firstly a promise for now: a promise to master problems way faster than a how a classical computer would.

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Well, easily explained; if you want to build a Quantum Supercomputer, in many cases you need to be ready to cool it down to temperatures below -270C.

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It’s ultra cold dear, like nowhere else in the Universe. If classical computers look like boxes with blinking lights and USB ports, a Quantum Supercomputer is a chandelier in a large pipe surrounded by noisy vacuum pumps and cryostats, consuming lots of energy and requiring lot of space. I know that cause I have been recently visiting a few, all because of my job as technical marketing manager at Tektronix.

There’s countless problems engineers try to solve with Quantum Computing, but the ones we have been asked to help with refer to the need of controlling highly complex and entangled quantum states.

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Ok, back to classical computers: my niece is now familiar with transistor-based circuits and microprocessor having visited my messy room/lab/office for a while. She knows how a physical bit is made in a classical computer. But what about a Qubit? How do you practically make it?

Here came to rescue me a recent customer visit I made where ionized atoms were used to implement “physically” a Qubit. They call them “Ion traps”.

I asked my niece to mentally visualize an atom acquiring a negative or positive charge by gaining or losing orbiting electrons occupying various energy levels represented as concentric circles.

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I asked her to keep visualizing this image in her mind and imagine now a strong invisible force like a laser beam or an electromagnetic field keeping these ions in a way that they were “trapped”, i.e. preventing them to interact or couple with other atoms in the environment.

This is a great starting point for imagining using these trapped ionized atoms to create a Qubit gate similarly to the logic gate based on transistors she started to be familiar with.

Imagine that a pair of electrons orbiting around the trapped atom for a sort of tiny dipole, and that the dipole moment is the Quantum state we want to set in order to program our Qubit gate.

Electrons are perfect suitable entities to implement a Qubit: they have a degree of freedom (spin) which could represent a quantum two-level system by itself. We embed them in a trap to keep them as “still” as possible and control them, using the trap to keep them separated by other atoms.

Of course we need to create vacuum in it, since air particles are also atoms that can interact with them.

The more we can isolate them, the longer we can retain the Quantum “information”. When I say longer, I mean seconds or less.

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Nope, there other ways to implement this, but I the one I am explaining now, information is retained for microseconds only. This is the case of creating a Qubit gate with Superconductors; the so-called superconducting Quantum computers.

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I told my niece to imagine a very tiny piece of metal, so tiny that the technology to build it is called nanotechnology. I asked her to imagine this tiny piece of metal being aluminum and being looped like an oscillating spring. I told her the name of it is anharmonic oscillator, but she immediately forgot it.

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I told her about the electrons in this magic spring spin, so we have the same thing as before, degrees of freedom to store a quantum information in. Now I told her that depending on how I fabricate this spring, I can decide how the energy level in which the electrons can stay are spaced.

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So I responded that yes, the magic spring behaves like a big atom in this sense, with the difference that I can fabricate myself this big atom with nanotechnology and design how these energy levels are spaced and organized.

I then asked her to imagine several magic springs coupled and resonating ( I actually said wiggling) together. I told her that shortly before she had birth, a scientist imagined and realized this multi-magic spring structure and called it transmon.

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These magic things resonate if coupled with something like a strong electric field. Again, I told her this need to be cooled down very much, so this tiny little thing needs to be kept in a large and noisy fridge that consumes a lot of energy.

I told her that putting hundreds of thousands of these magic things together the create a bigger and more powerful quantum computer would require to increase the size of the fridge, and that this problem called scalability is a big one to solve.

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I told her that there is a way to create Qubits in a different way that does not present this problem. It is called Neutral Atoms and the principle is very similar to the Ion Trap I explained first. In this case atoms are trapped by optical laser beams. The good aspect here is that things are way more compact that in the superconducting case. She could visualize it and she finally started understanding.

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Well this box called AWG, arbitrary waveform generator, is part of what you need to manipulate, program and control the Qubit gate you just imagined.

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Let’s go back to the visual image of the Qubit dipole that “vibrates” according to quantum mechanics. We want to control these vibrations and the modes this dipole can orientate.

So we take a microwave source …

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…and we mix this wave with the signal coming from the AWG (that we decide how they must look like) and what comes out we use to shape the laser beam we mentioned before to trap the ions into pulses.

These pulses should drive the motion of the ions along specific trajectories we want to design this quantum logic.

AWGs can shape things the way we want, microwave pulses, optical laser pulses, anything. This helps scientists to design the traps we spoke about. Or in the case of the magic transmon spring, to control the way it oscillates.

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