so we have been dealing with implementation of quantum computers in the last week we went
through the idea of ion trap implementation of quantum computing we will finish it off
this week by looking at how these quantum computing options have now been attempted
into the commercial angles and we will then go forward to the other more advanced approaches
of quantum computing that have been done
so last week we dealt with ion traps as one of the important aspects of quantum computing
implementation this week we will summarize our findings and discussions that we did on
quantum computing using iron traps and then we will look into the other techniques some
of which are now being attempted commercially so let us look at what we have done last week
in terms of the bits in action we looked at the trapped ions and trapped ions are electrically
charged atoms or ions that have quantum energies that depend on the location of electrons tuned
lasers are used in this particular case to trap the ions and some other lasers can
also be used so that they can be put in to super position states
often it's not the single laser which is going to do the trapping and cooling of the
laser as well as doing the superposition so in the sense one of the problems which happens
in this particular approach is at several lasers are used for this thing to work effectively
however this has many advantages it the ions are long lived and they can be greater than
thousand seconds they they are success rate of the logic is also quite high it's ninety
nine point nine percent success in terms of logic applications the total number of
entangled states that have been shown to be successfully achieved with this technique
is as high as fourteen so that's a that's in fact the highest number of qubits in real
sense that have been used directly in terms of implementation
so there has been a lot of affect as a result of this huge success in terms of using this
technique commercially and in the rays to build quantum computer companies are perusing
many types of quantum bits or qubits each of which have been their own strengths and
weakness and as we mentioned here ions trap definitely has seen it's benefits and as result
of this um brand new company called ionq has been setup to look into this commercialization
of ion trap scheme of quantum computing
we already know that academic researches use far more varieties and options but as
far as companies are concerned for commercialization they would be taking approaches where the
principles can be scaled and so that way ion trap has a huge benefit in terms of the number
of entangle qubits is quite high in this case
the advantages are clear they are very stable and it also has the highest achieved gate
fidelities ninety nine point nine percent however on the other hand it actually has
a fairly slow operational procedure and as i mentioned in the beginning here that
there are many lasers that are essentially needed for
this particular concept of ion trap base quantum computing to be successful anyway because
it has become commercially viable let us look in to this new ionq company
which has brought in the concept of trapped ions as commercial approach to a quantum
computing
here is a latest news taken from last years december issue of science where they ran
a news article saying that scientist are closed to building quantum computer that can
beat the conventional one and this is based on the ion trap one so the this is a
picture taken from the lab of the university of maryland college park physicist chirs monroe
who is one of the co founders of ionq the company it's a quantum company startup
that examines equipments that keeps ions in long lasting quantum states the other co founder
jungsang kim is an electrical engineer at duke university durham north carolina
so that's one of the points which i wanted to point out here is that quantum computing
is now coming to a point where commercialization is becoming a practicality and in this
respect let us now look at one of the companies which claim in to being in terms quantum computing
quite early in in it's development and has been successful in one way or the other
over the years and this particular company is a canadian company i think i have mentioned
about it earlier in the introductory sections is known as d wave
now in the next several slides that i will go through discussing about the d wave um
computer would be very very much in tuned with what it is present in their website
so let us look at the d wave quantum computer so this is the one of the newer versions which
they call as the two x version so that d wave two x quantum computer has a the detail
of their technology overview and it's available in their website
so as you can see it was one of the first ones founded in nineteen ninety nine as a
point out quite correctly is of worlds first quantum computing company their mission has
been to integrate discoveries in physics engineering manufacturing and computer science in to breakthrough
approaches to computation to help solve some of the worlds most challenging computing problems
it is true that today d wave is recognized in the development fabrication an integration
of superconducting quantum computers their systems are being used by many organizations
and institutions including lockheed martin google nasa and the university of southern
california d wave has been granted over hundred and twenty five u s patents and has published
over eighty scientific papers many of which appeared in leading science journal
in fact earlier in february this year um there was a paper which in used the d wave quantum
computing to report very large number of qubits sixty four qubits to be precise
of which in reality the practical number of qubits that they were able to use for computing
was much lower but it does have a lot of advantage they do admit that it is actually the beginning
of quantum computing as we know however having these commercial developments really
make a huge advantage so let us look in to them a little bit
so in order to speed computing these quantum computers which they have build are based
on the idea of super conduction qubits as they mentioned so here is little bit of the
detail of how the quantum computing as we have been talking about considers the qubits
to be encoded in terms of zeros and ones simultaneously and the superposition of the states along
with the quantum effect of entanglement are the once which go ahead in terms of using
their developments for quantum tunneling enable quantum computers to consider and manipulate
many combinations of bits simultaneously the d wave two x processor has thousand qubits
and therefore can evaluate two to the power thousand possible solutions at the same time
there are questions in reality about how exactly
all of these could be put to you as i just mentioned earlier that although a lot of
these qubits can perhaps be put to use or can be shown to exist their usage in actual
computing is often not really use
so in some sense we can say that there are lots of ancilla qubits which can be available
in this kind of operations so let us see how this has been successful so in terms of the
computing with this kind of d wave computer this system implements a quantum annealing
algorithm which solves problems by searching for the global minimum of a function so this
works in a different principle from many of the processors that we have been discussing
earlier and this a fundamentally different from the familiar frame work of classical
computing built on logical operations but it is relevant in many high value problems
such as minimizing error or in a voice recognition system controlling risk in a financial portfolio
or reducing energy loss of an electrical grid
the concept of using quantum annealing for finding global minimum of a function
has also been often used earlier for quantum simulations and classical computers and that's
a quite a popular technique for m d super positions for many of the chemists while there
are different ways in which users can submit problems to the system and at the level of
the machine instructions of the quantum processor the system solves a quadratic unconstrained
binary optimization problem as they call it qubo where binary variables are mapped
into qubits and correlations between variables are mapped to couplings between the qubits
the system of interacting qubits is then evolved quantum mechanically via the annealing algorithm
to find the optimal or near optimal solutions
so that is typically the way how their particular concept of quantum computing works and
visually this is a more interesting to note that it's like a landscape on which there
are many many possible minima although the global minima as you can see is a only one
however there are many other local minima where the system can get stuck and that's
one of the most important things of how to find out the right solution so the sol solving
problems with the d wave system can be thought of as trying to find the lowest point in the
landscape of peaks and valleys every possible solution is mapped to the coordinates of the
landscape and the altitude of the landscape is the energy or cost of the solution at that
point with aim is to find the lowest point or points on the map and read the coordinates
as this give the lowest energy or optimal solution to the problem
so in order to do that what is a important is to figure out that the gap that can be
achieved for example to reach the lowest minima as it looks like in this particular case
this particular point is to find out that the energy or the cost function as they
define it is the one where the maxima is at least in this particular visual graphics at
this point where which should also correspond to let say the maximum difference from the
mean position of the starting face so that's how this is done
and one of the most important issues about this particular approach is to ensure that
hm the system does not get stuck in local minima so the special property of quantum
physics so in this case this special property of quantum physics such as quantum tunneling
allows the quantum system to explore this landscape in ways that has never been possible
with classical systems so in classical systems what would happen is it would be each and
every point of the minima would be explored one at a time minima or maxima and then based
on the number of attempts this has been done the solution can be good or bad
quantum tunneling on the other hand is like a layer of what are that covers the entire
landscape you can visualize it in that way as well as running over the surface water
can tunnel through the mountains as it looks for the lowest valley the water is an analogy
for the probability that a given solution will be returned when the quantum computations
occur the water or the probability is pooled around the lowest valleys the more water in
the valley the higher the probability of that solution being returned a classical computer
on the other hand is like a single traveler exploring the surface of a landscape one point
at a time
so that's the simultaneous nature of this problem which essentially makes the quantum
process much more effective the analogy of several solutions being looked at simultaneously
as had been also talked about in terms of grover solution is one of the ideas which
quantum physics addresses very effectively and that is being utilized in terms of this
quantum annealing process to get the right answer so that is the basic idea behind this
in terms of the actual computer it sort of looks like this where the physical foot
print of the system is about ten feet by seven feet by ten feet in terms of it's
length width and height it houses a sophisticated cryogenic refrigeration system because we
are talking about very low temperatures shielding an input output systems that support a single
thumbnail sized quantum processor
so the essential final quantum processor is only a thumbnail sized one however it needs
this big of a footage to achieve of the principles of the low temperature and then the shielding
as well as the ion system most of the physical volume of the current system is due to the
size of the refrigeration system and to provide easy service access
so in order to for the quantum effects to play a role in computation the quantum processor
must operate at an extreme isolated environment that's one of the issues that is always an
point in terms of quantum computing the refrigerator and many layers of shielding creates an internal
environment with a temperature close to absolute zero that is isolated from external magnetic
fields vibrations and external r f signals of any form the adjoining cabinets contain
control subsystems and the front end service that provide connectivity to the system the
d wave two x system can be deployed as a part of high performance computing data center
using standard interfaces and protocols
so this is the current commercial system which exists and the way it is being used
by other users as well as multiple users point of time is through this kind of a um
operational procedure whereas we already saw the picture in which the shielded and closer
has the quantum processor as we talk about it and the next one is slightly smaller or
foot print part is you having the control and sub system and service the quantum processor
as i mentioned is only about a thumbnail sized but which is kept inside the pulse tube
dilution refrigerator which is the part which takes most of the space and it's completely
shielded otherwise it would get into a lot of problem so that's the basic idea behind
this the schismatic of this picture which shows how this works and this can be then
controlled through another computer as well as a server which can then serve many other
remote users or regular p c interfaces
so the major part of this as a as as been mentioned is the temperature controlled part
where the processor is kept at near zero temperature so the idea here is that the processor is
in fact kept at colder than interstellar space in order to achieve that this is the sort
of the layering system which is done to ensure that the processor is really completely shielded
in terms of the conditions as well as the temperature required is achieved as a result
of this particular way of the geometry so there the temperature in the quantum processor
is reduced to near absolute zero which is required to isolate it from it's surroundings
so that it can behave quantum mechanically so that's one of the most important things
um which technology needed to make sure that it works in general the performance increase
as the temperature is lower the lower the temperature the better is a performance the
d wave two x processor operates at a temperature of fifteen milli kelvin which is approximately
hundred and eighty times colder than interstellar space
the refrigeration system used to cool the processor is known as dry dilution refrigerator
it uses liquid helium in a closed loop cycle in which it is recycled and re condensed using
a pulse tube cryocooler the close loop refrigeration removes the need for on site replenishment
of liquid helium and makes the system suitable for remote deployment so the closed loop cooling
is essential to make sure that the liquid helium could be reused and can be used
remotely while the dilution refrigerators are not uncommon in research environments
d wave has advanced the technology to ensure long life and reliability and this is one
of the technology development such as made this kind of a quantum computer possible
as the cooling power available at such low temperatures is extremely low d wave has taken
great care to minimize the heat loads and efficiently manage the heat transfer within
the system so these are design aspects that they had to actually engineer to ensure that
such a system can operate at such very low temperatures at sustain it there despite
the extreme environment inside the system the d wave quantum computer can be located
in standard data center environment so that is one of the major developments that they
have manage to achieve and that as it shown here is partly possible because of the way
they have done these stratification of the temperature processor starting at room temperature
throughout the temperature decreases at each level until it is close to absolute zero where
the processor itself is located
so the main part of the system definitely then relay on the input output shielding and
the materials this by the way is the logo of the d wave so the i o system is responsible
for passing information from the user to the processor and back after receiving a problem
from the user via standard web protocols the data is converted to analog signals and carried
on normal conducting wires that transition to superconducting wires at low temperatures
the requirements for the input output and shielding subsystems placed many unusual demands
on the design materials and manufacturing processor required that is typically expected
the i o system was design to filter out essentially all unwanted noise functions at milli kelvin
temperatures and withstand multiple warming and cooling cycles between room temperature
and base temperature
the current input output system in their case uses two hundred heavily filtered lines from
the control electronics to the processor so from the control electronics to the processor
they are about two hundred heavily filtered lines that was specifically designed for optimal
system performance the system also includes a variety of superconducting metals which
often require unusual and non standard manufacturing techniques in addition none of the materials
close to the processor can be magnetic so this is this is actually another very important
aspect that they have to worry about that near the processor nothing can be magnetic
in their sense
as the quantum processor is adversely affected by stray magnetic fields extreme care had
to be take to exclude them the magnetic shielding subsystem achieves fields less than one tesla
across the processor in each axis this is the approximately fifty thousand times less
than the earth magnetic field this low magnetic field environment is achieved with a system
comprised of multiple shields some of them high permeability metals and some of them
superconducting
the system sits inside a shield enclosure that screens out r f electromagnetic noise
so all kinds of radio frequency electromagnetic noise is sort of shielded off because of the
shielding enclosure the only path was signals between the inside and the outside of the
shielded enclosure is a digital optical channel carrying programming information in and results
of computations out the processor resides in a high vacuum environment in which the
pressure is ten billion times lower than atmospheric pressure
so essentially this is a environment which is often what we have used for many conditions
under the n m r well the n m r doesnt need that level of vacuum um but ion traps for
instance have similar environments that are often necessary so this is basically the principle
which they have done is that they have essentially made the inside of the computing environment
so shielded and so correctly available so that the principle of quantum computing
or the quantumness can be preserved
so in spite of all this they have manage to do a few important aspects which are necessary
which is the power requirements have been kept to a normal level unlike the traditional
super computers that generate massive amounts of heat and require huge amounts of power
the d wave system is based on superconducting electronics so the superconducting electronics
is um is an important part of this process that do not require heat dissipation and require
little power supply
the d wave two x consumes less than twenty five kilo watts of power most of which is
required for cooling and operating front end servers as more powerful quantum processors
are released this power requirement will remain low so this is one of their claims and they
have been managing to do that which is very important because otherwise the power requirement
can create other issues which they are trying to avoid the system requires water cooling
but the amount of water needed is on power what a kitchen tap can provide the amount
of air conditioning needed is also a tiny fraction of what is expected in a data center
given the footprint of the system
so this is one of the important parts which they have also had to build up to make sure
that it is a possible to be put in to a regular computing environment where the classical
computers reside so now the main part which is the quantum processor which requires
all these shielding's and all these advantage of putting it away from everything so the
d wave quantum processor is built from a lattice of tiny loops of metal niobium each of which
is one qubit computer it's a lattice of tiny loops of metal niobium each of which is one
quantum bit or qubit
so i will show it to you in a slightly more detail in the next slide here it is perhaps
the the whole processor is shown but the highlighted parts that would be shown in in in the next
slide with the outline red when then niobium i cooled down below nine point two kelvin
it becomes a superconductor and starts to exhibit quantum mechanical effects so that
is the principle which is used behind this quantum computing device of the d wave
by circulating currents either clockwise or counter clockwise the superconducting qubit
emits a magnetic field pointing downward or upward encoding a logical one or zero and
that's one of the reasons why they have to be so careful about shielding it in terms
of magnetic fields so a because this is operated mostly in terms of a the magnetic field a
creating the logical a qubit one or zero it has to be very highly shielded
during quantum annealing current flows clockwise and counter clockwise simultaneously this
enables the qubits to be in a superposition state that is both in a zero and one at the
same time at the end of the quantum annealing cycle the qubit collapses into one of the
two states either zero or one so the preparation phase in this case essentially involves applying
the circulating current clockwise or counter clockwise to create the superconducting qubit
in terms of a magnetic field pointing upward or downward creating the logical zeros and
one and that is the part which is your preparation and then the quantum annealing process which
where the processing occurs current is flowing either clockwise or counter clockwise simultaneously
and this enables the quibts to be in the superposition state and when the computation is done then
it finally collapses to one of the two states either zero or one and thus the magnetic field
with essentially be either pointing upward or downward or in other one sense there would
be a clockwise or a counter clockwise signal in terms of circulating current
so these are the various taps in it and as i mentioned here is the detail of these red
lines where in the niobium metal is been shown in the actual processor so as i was mentioned
here one quantum qubit or is shown outlined in red so these are the tiny loops of the
metal niobium so here are the tiny loops of the metal niobium which are essentially showing
the qubit so the processor is sitting as mentioned at the colder zone that is being amplified
to show the qubits in the red
so in order to go from a single qubit to a multi qubit processor the qubits must be connected
together to exchange information this is achieved through the use of elements known as couplers
which are also made from superconducting loops putting many qubits and couplers together
with control circuitry to manage the magnetic fields create a fabric of programmable quantum
devices after the computation has finished and the qubits have settled into their final
zero or one states which is generally the classical condition the values held by the
quibts are returned to the user as a bit strings of zeros and ones because by that time everything
information is classical
the d wave two x system is based on a fabric of thousand plus quibts and over three thousand
couplers in order to attain this scale the processor contain over one twenty eight thousand
josephson junctions believed to be the most complex superconductor integrated circuits
ever built so that is the claim which the d wave system makes in terms of what they
have managed to achieve in terms of one thousand plus qubits
to complete the story about the d wave computer in terms of it's commercialization i would
like to point out the software and the programming aspects in their case and comes with the help
of a web api with client libraries available for c c plus plus python and matlab the most
common programming environments this interface allows the machine to be easily accessed as
a cloud resource over a network using development tools and client libraries users can write
codes in the language of their choice and then interface it with the available ones
as described below the users can submit problems to the sub system as described the users
can submit problems to the system in a number of different ways values corresponding to
the weights of the qubits and coupling strengths of the interaction between them are submitted
to the system which then executes single quantum machine instructions for processing the solutions
are values that correspond to the optimal configuration of the qubits found or the lowest
points in the energy landscape these values are returned to the user program over the
network
because a quantum computer is probabilistic rather than deterministic multiple values
can be returned providing not only the best solution found but also other very good alternatives
from which to choose users can specify the number of solutions they want the system to
return so these are some of the advantages or additional options that the quantum processor
can provide which are provided by them
there are multiple ways to submit a problem to the d wave quantum computer as mentioned
in the last slide these are the many different ways one can use a higher level programs in
c c plus plus python or matlab to create and execute a quantum machine instruction use
one of the d wave tools under development including qsage a translator designed for
optimization problems toq a high level language translator used to constraint satisfaction
problems and designed to let users speak in the language of their problem domain or directly
program the system by using quantum machine language to issue the quantum machine instructions
so these are the various different ways how are these particular system can be connected
to and programmed to submit their problems
so in a sense the overall system looks in the environment of the d wave software
environment looks like this they have the different processors available at different
level so the optimization usage a qsage constraint satisfaction uses toq and there are many others
that can be sampling ml these are the different translators that can be used there are lots
of host libraries which can be of a different kinds as we mentioned as well as there
are various different independent representations and the comment line interfaces as well
as quantum machine instructions
so these are the various different ways of interacting with the machine and many of the
developments so for example this one and this one mentioned in this particular slide
taken from their website essentially mean that they are the under development for feature
capabilities only the direct solid lines are the ones which have been used currently so
generally speaking this qubo is currently developed the c c plus plus python matlab
these are developed direct quantum machine instructions are developed the rest of the
devices which are in dotted forms are being developed and finally the instructions
are provided to the target system which is a quantum um system which does the operations
of quantum annealing and gives the best possible result as well as several close enough results
which can be utilized
so basically this whole principle is based on superconducting loops and this is
the idea of a resistance free current that oscillates back and forth around a circuit
loop an injected microwave signal excites the current into super position states and
this can be put into a lot of a developments and this is one of the principles and it's
associated environments which sort of gave rise to the advantageous that we discussed
as of now the point to remember however is that as i mentioned earlier this number has
changed very recently
however these numbers are the real possible entanglements which have been achieved although
there are many mores states which can be available the longevity of these states
are not very high but it is long enough to take advantage of many of the processors
now this particular superconducting loop approach is slightly different from the principle of
d wave that we discussed which use the quantum annealing approach however one of the advantage
of these is that it is open source as of now for many other companies to look at and therefore
google ibm and quantum circuits are looking at these kinds of approaches or looking at
it now this has the advantage of fast working and it's build on the existing semiconductor
industry
the disadvantage here is that the collapse is easy and should have been kept cold so
many of these quantum computing approaches as i have been talking about a pl[ate]- um
including the most commercially successful d wave ones have their difficulties um and
there are commercial attempts which are being attempted at many different cases so the d
wave system which use the quantum annealing method of going from the josephson junction
approach of producing quantum states and going ead with this has been more successful till
date in terms of commercial
the other ones are coming into the picture and before i close todays lecture let me actually
tell you about the few other approaches in which i have already mentioned the superconducting
loop one which is similar to in principle to the one that d waves are using although
the d wave essentially makes the advantage of the principle of quantum annealing on top
of it to achieve the number of entangle states and others
however as you understand the approach of quantum tunneling to get quantum computing
is different from what people would and discuss in terms of the way we have developed and
discussed in terms of quantum computing so there are lots of questions on the d wave
system although it is been used in many places the more traditional approach of using the
same scheme um it does not use quantum annealing essentially you would be what this other part
which i just discussed in terms of semiconductor loops talk about where there are other
companies which have now started looking into this process hence seeing how this can be
taken into next level as it also involves the advantage where it is based on the
existing semiconductor industry
however all of these as in the d waves have shown would require the maintenance of very
good quality refrigeration and the isolation so that it can be kept cold and is not
going to interact much with other states the other area where a lot of effort has been
put in in terms of commercial basis is the silicon quantum dots these are artificial
atoms made by adding an electron to a small piece of pure silicon the microwaves control
the electrons quantum state in this particular case this has a fairly long longevity point
zero three seconds and the logic success rate is also reasonable ninety nine percent
however the scalability has not yet been achieved much only two qubits which have been
shown to be entangled as of now and again this needs to be kept cold and is the difficult
of this however this is also a stable system and it's build on existing semiconductor industry
so this is another one of these approaches which is been supported through intel um ibm
for example which is going ahead with the semiconducting loops has declared that
sometime later in this year they are going to come up with their version of quantum
computers um and the silicon quantum dots in another area where as i just mentioned
lot of effort is going on and intel is gearing up more on this direction other
approaches which are also been explored and there are two more which i have been mentioned
here before i close todays lecture and those are one of them is known as the topological
qubits which are supposedly one of the most sort after concept although it is very
new and therefore not much development has been achieved
however this has a very interesting principle because it is based on the idea of quasiparticles
which can be seen when the electrons are channeled through semiconducting structures
their braided paths can encode quantum information and the advantage of this is that
it has a the huge reduction in error processing however it's exist in this is all in theory
as of now and it's existence and other details in terms of longevity logic success and number
of entangled are not yet available and microsoft and bell labs are basically pursuing this
kind of effort
the other one which have been shown to exist and a quite a few entangle states have been
achieved is the vacancy states inside diamond a nitrogen atom and a vacancy add an electron
to a diamond lattice and it's quantum spin state along with those of the nearby carbon
nuclei can be controlled with light now this is also another area where in this quantum
diamond quantum technologies it is a company which has come on to try to operate that and
this advantage the biggest advantage of this that it can operate at room temperature most
of the other techniques that we have been talking about all this time requires very
low temperatures and stability and isolation is one of the biggest issues but this one
can operate at room temperature and can be addressed with light it has a long longevity
ten seconds i mean not has high as entraps but fairly long and it has a fairly decent
success rate logic in it's success rate in terms of ninety nine two point two percent
and as of now about six qubits have been shown to be entangled
so the difficulty however in this case is to entangle the state and keep it at that
level the in all these cases one of the things which when whenever we have mentioned longevity
it's basically means that the record coherence times for a single qubit superposition state
and where as the logic success rate is the highest reported gate fidelity for the logic
operations on two qubits and the number of entanglement is the maximum number of qubits
entangled and capable of performing two qubit operations so these are the basic principles
and the basic schemes and tec qubits which have been brought into the commercialization
angle as mentioned there are earlier there are many other approaches to quantum processing
which have been attempted in the laboratory procedures in an the academic circles but
these are the few which i thought would be represented would be a good idea to present
it all together which are in terms of commercialization so that you can all look at the commercialization
angle of quantum computing in one short
so this is what i tried to present in todays lecture so in the lecture we will go into
more of spintronics which i talked about in the last week and we will take it from
there so see you in the next lecture