IACS Research Day Faculty Talks: Predrag Krstic
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IACS Research Day Faculty Talks: Predrag Krstic


>>Okay, so yes I have been doing many things
outside class to different areas of physics, starting with math for the processes. And I’ve found cohesions, molecular cohesions,
[inaudible] physics, all of interest for, you know, profusion. And then microelectronics, obviously flowing
inside the nanotechnology, and then DNA in electrolyte, quantum physics of interest for
DNA sequencing. And when about here and something ago, I saw
— well saw — learned a little bit on quantum computing, something started burning in myself,
so I thought, “This is it; this has the common ingredient that — of everything that I have
been doing before,” and the common word is “quantum mechanics”. Okay; so yes let’s start with some computing
words. So what is “algorithm” is a set of instructions. And the discovery of algorithms that would
work much better on quantum computing really somehow [inaudible] the widespread interest
in quantum computing. And after finding there is a series of names
that were developing such algorithms, and essentially always stating, “Yes, quantum
computing would work much more fast in the tasks of computing [inaudible], okay? And what is the basic work in quantum computing
is acute. [Inaudible] is quantum bit, okay? And while bit can have value zero and one,
[inaudible] can have a value between zero and one. It’s actually a combination of these two computational
basic states [inaudible]. So the basics elements of a quantum computer
are the unit of information that act on this [inaudible] called “gates”. These are really operations, okay? And a set of single qubit gates and even the
one double qubit gates like C naught is enough to make [inaudible], in two instances, like
in classical sense, okay? So what are the elements of the algorithm? So you define initial state of your qubit,
okay, [inaudible] operations on them. And then you read out the results on your
qubits after applying the series of operations. And that’s it, okay, like any other computation. Now, where the quantum content — where is
the quantum content here? Well, first, quantum systems can exist in
[inaudible] positional states. [Inaudible] that’s not particularly quantum
feature classical system [inaudible]. But this effect really allows [inaudible]
computation that can be done in one step, and cannot be done by a computer. So when you do measurement of a qubit alteration,
okay, you redefine a qubit of one state in one bit with some probability, okay; which
means so that you lose practically the quantum nature and the system is compressed into a
classical meaning of a bit, okay? So what are the elements of quantum and classical? Well, the system AB, okay, is a contingent
product of A and B in classical. In quantum, it’s a tenth of a product, okay? So that’s a really essential difference. And each difference really introduces another
thing that follows from this, it is a so-called “quantum entanglement”, okay? So two states of A and B that are not a product
of A and B in a classical sense are really entangled. And just as a demonstration of [inaudible]
product, okay; so this is a two qubit situation, okay? So possible states are obviously all combinations
zero and one, zero and four, four, that’s two, two squared, okay? So [inaudible] without anymore words is a
[inaudible]. And from there it follows that the states
in these two products of this single state are now [inaudible] elements for basics affected
by their [inaudible] zero, zero, and so on. So you start in one qubit to two, two, one,
okay? With two qubits, you have four states. For three qubits, you have two to the three
generally for end states — and qubits, sorry, you have two to the end. Okay? So a little bit more play with [inaudible]
of quantum. I would betray myself if I wouldn’t try to
be deductive and [inaudible] and deductive [inaudible] sense. But anyway, I try to talk about this fine
computing. So what are the [inaudible]? For example, self-organizing of molecules,
okay, organizational [inaudible], physics, people, units, and rank. So the [inaudible] interaction you arise to
the [inaudible], okay? And that induces order, induces [inaudible]
operations are drawn into microscopic difference, okay, which is often unpredictable. This is difficult to control. That’s true for quantum system [inaudible],
okay? Now, as I said, the [inaudible] principle
is one feature of quantum system. So for any two, let’s say yellow and blue
states, [inaudible], okay? These sometimes appear yellow or blue of — thank
you. But they never appear as green. That is [inaudible], too, okay? So for uncertainty, as is often used as the
word in quantum mechanics, okay? So the measurement projects the state of this
mixture, blue plus yellow into one of the colors, into one of [inaudible] states, yellow
or blue. And the [inaudible] so we can compute it,
it collapses the [inaudible]. Entanglement follows [inaudible]. If you have two quantum systems, one and two,
each can be in a particular state, yellow or blue. The compounds [inaudible] to a position state
one, two, okay, less two, one, okay? And if you observe one, we don’t have any
need to look at two and to measure two because you know that if your observation is one,
the other state is definitely blue; or if you observe two, this will be one, okay? And so this is an example of an entangled
state, okay? So you know the information of the other partner
of the entanglement if you measure the one first. And this is bringing another feature of quantum
mechanics, which is [inaudible]. And in 1935, that really confused Einstein,
who I thought — okay which are — okay I will stop. Sorry. [Laughter] Who thought it was quite spooky,
okay, two particles that are not interacting are following each other by some hyper or
hypo universe lines, okay? And we have to accept that this is really
the future, a future of quantum mechanics, whatever we understand about that. So it’s your choice. So therefore, the real quantum computer is
the one that can be entangled, okay? So all qubits that are active in quantum computer
are entangled. If they are not, if it’s not a quantum computer,
okay. And now there are other issues if they are
not or they are partially, you have errors produced. And so issues of fidelity and [inaudible]
is a principle issue that is currently a big headache for quantum computing. And
you probably saw a poster of Yun [assumed spelling] who was talking exclusively — Yun
[inaudible], my grad student who was talking exclusively about this problem of errors. So that’s about the dream and reality. So the dream is to have quantum computing,
the reality is too many errors currently. And it has to be resolved in different ways. It’s also had a problem which is a problem
of the fact that each computing [inaudible] system so it interacts with the environment,
and therefore, the coherence is one of the fundamental issues. Thank you. [ Applause ]>>Questions?>>At the end, you just mentioned that the
coherence is an issue and there are too many areas. Are you confident that those are [inaudible]
that we overcome in the next ten, 20 years? I mean, what’s the timeframe do you think
on –>>Okay; so you are asking me about [inaudible].>>Yes. [Laughter]>>Okay; so I’m, let’s say, agnostic in that
sense, okay? So which means yes I do believe that it won’t
happen in two years like many people say, but I agree that it could happen in ten years
with the reason with probability. Okay.>>Thank you.>>Okay, thank you again, [inaudible].>>Okay. [Applause]

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