1
00:00:00,195 --> 00:00:03,313
For most of our history, human
technology consisted of

2
00:00:03,313 --> 00:00:06,051
our brains, fire, and sharp sticks.

3
00:00:06,631 --> 00:00:10,102
While fire and sharp sticks became
power plants and nuclear weapons,

4
00:00:10,102 --> 00:00:12,692
the biggest upgrade has
happened to our brains.

5
00:00:13,132 --> 00:00:17,619
Since the 1960s, the power of our brain
machines has kept growing exponentially,

6
00:00:17,619 --> 00:00:21,794
allowing computers to get smaller
and more powerful at the same time.

7
00:00:22,524 --> 00:00:25,444
But this process is about
to meet its physical limits.

8
00:00:25,834 --> 00:00:28,721
Computer parts are approaching
the size of an atom.

9
00:00:29,391 --> 00:00:32,689
To understand why this is a problem,
we have to clear up some basics.

10
00:00:39,666 --> 00:00:43,903
A computer is made up of very simple
components doing very simple things,

11
00:00:43,903 --> 00:00:48,474
representing data, the means of processing
it, and control mechanisms.

12
00:00:49,064 --> 00:00:50,678
Computer chips contain modules,

13
00:00:50,678 --> 00:00:53,906
which contain logic gates,
which contain transistors.

14
00:00:54,556 --> 00:00:58,459
A transistor is the simplest form
of a data processor in computers,

15
00:00:58,459 --> 00:01:01,555
basically, a switch that
can either block or open

16
00:01:01,555 --> 00:01:03,479
the way for information coming through.

17
00:01:03,939 --> 00:01:08,463
This information is made up of bits,
which can be set to either zero or one.

18
00:01:09,073 --> 00:01:12,982
Combinations of several bits are used to
represent more complex information.

19
00:01:13,502 --> 00:01:18,025
Transistors are combined to create logic
gates, which still do very simple stuff.

20
00:01:18,025 --> 00:01:22,888
For example, an AND gate sends an output
of one if all of its inputs are one

21
00:01:22,888 --> 00:01:25,104
and an output of zero otherwise.

22
00:01:25,664 --> 00:01:28,982
Combinations of logic gates finally
form meaningful modules,

23
00:01:28,982 --> 00:01:31,066
say, for adding two numbers.

24
00:01:31,446 --> 00:01:35,134
Once you can add, you can also multiply,
and once you can multiply,

25
00:01:35,134 --> 00:01:36,851
you can basically do anything.

26
00:01:37,481 --> 00:01:41,038
Since all basic operations are literally
simpler than first-grade math,

27
00:01:41,038 --> 00:01:43,729
you can imagine a computer as
a group of seven-year-olds

28
00:01:43,729 --> 00:01:46,038
answering really basic math questions.

29
00:01:46,578 --> 00:01:50,717
A large enough bunch of them can compute
anything, from astrophysics to Zelda.

30
00:01:51,277 --> 00:01:53,617
However, with parts
getting tinier and tinier,

31
00:01:53,617 --> 00:01:56,049
quantum physics are making things tricky.

32
00:01:56,649 --> 00:01:59,805
In a nutshell, a transistor
is just an electric switch.

33
00:02:00,105 --> 00:02:03,111
Electricity is electrons moving
from one place to another,

34
00:02:03,111 --> 00:02:07,818
so a switch is a passage that can block
electrons from moving in one direction.

35
00:02:08,408 --> 00:02:11,678
Today, a typical scale
for transistors is 14 nm,

36
00:02:11,678 --> 00:02:15,481
which is about 8 times less
than the HIV virus’s diameter

37
00:02:15,481 --> 00:02:18,451
and 500 times smaller
than a red blood cell’s.

38
00:02:18,931 --> 00:02:22,497
As transistors are shrinking
to the size of only a few atoms,

39
00:02:22,497 --> 00:02:25,929
electrons may just transfer themselves to
the other side of a blocked passage

40
00:02:25,929 --> 00:02:28,173
via a process called quantum tunneling.

41
00:02:28,643 --> 00:02:31,649
In the quantum realm, physics
works quite differently from

42
00:02:31,649 --> 00:02:33,358
the predictable ways we’re used to,

43
00:02:33,358 --> 00:02:36,561
and traditional computers
just stop making sense.

44
00:02:37,071 --> 00:02:40,935
We are approaching a real physical
barrier for our technological progress.

45
00:02:41,655 --> 00:02:44,001
To solve this problem,
scientists are trying to

46
00:02:44,001 --> 00:02:47,016
use these unusual quantum
properties to their advantage

47
00:02:47,016 --> 00:02:49,052
by building quantum computers.

48
00:02:49,664 --> 00:02:53,141
In normal computers, bits
are the smallest units of information.

49
00:02:53,611 --> 00:02:57,787
Quantum computers use qubits, which
can also be set to one of two values.

50
00:02:58,287 --> 00:03:00,613
A qubit can be any
two-level quantum system,

51
00:03:00,613 --> 00:03:04,290
such as a spin in a magnetic field
or a single photon.

52
00:03:04,580 --> 00:03:07,518
Zero and one are this
system’s possible states,

53
00:03:07,518 --> 00:03:10,678
like the photon’s horizontal
or vertical polarization.

54
00:03:11,148 --> 00:03:14,524
In the quantum world, the qubit
doesn’t have to be in just one of those;

55
00:03:14,524 --> 00:03:17,656
it can be in any proportions
of both states at once.

56
00:03:17,896 --> 00:03:19,905
This is called superposition.

57
00:03:20,355 --> 00:03:24,270
But as soon as you test its value, say,
by sending the photon through a filter,

58
00:03:24,270 --> 00:03:28,664
it has to decide to be either
vertically or horizontally polarized.

59
00:03:29,234 --> 00:03:33,722
So, as long as it’s unobserved, the qubit
is in a superposition of probabilities

60
00:03:33,722 --> 00:03:36,953
for zero and one, and you can’t
predict which it will be.

61
00:03:37,623 --> 00:03:41,690
But the instant you measure it, it
collapses into one of the definite states.

62
00:03:42,380 --> 00:03:44,537
Superposition is a game-changer.

63
00:03:45,267 --> 00:03:48,233
Four classical bits can be
in one of 2 to the power of 4

64
00:03:48,233 --> 00:03:50,040
different configurations at a time.

65
00:03:50,422 --> 00:03:54,400
That’s 16 possible combinations,
out of which you can use just one.

66
00:03:54,960 --> 00:03:57,016
Four qubits in superposition, however,

67
00:03:57,016 --> 00:04:00,202
can be in all of those
16 combinations at once!

68
00:04:00,875 --> 00:04:04,020
This number grows exponentially
with each extra qubit.

69
00:04:04,530 --> 00:04:08,110
20 of them can already store
a million values in parallel.

70
00:04:08,780 --> 00:04:11,680
A really weird an unintuitive
property qubits can have

71
00:04:11,680 --> 00:04:15,147
is entanglement, a close connection that
makes each of the qubits

72
00:04:15,147 --> 00:04:17,968
react to a change in the other’s
state instantaneously,

73
00:04:17,968 --> 00:04:20,084
no matter how far they are apart.

74
00:04:20,564 --> 00:04:23,254
This means that when measuring
just one entangled qubit,

75
00:04:23,254 --> 00:04:27,562
you can directly deduce properties of
its partners without having to look.

76
00:04:27,942 --> 00:04:30,718
Qubit manipulation
is a mind-bender as well.

77
00:04:31,118 --> 00:04:34,010
A normal logic gate gets
a simple set of inputs

78
00:04:34,010 --> 00:04:36,133
and produces one definite output.

79
00:04:36,654 --> 00:04:39,863
A quantum gate manipulates
an input of superpositions,

80
00:04:39,863 --> 00:04:44,780
rotates probabilities, and produces
another superposition as its output.

81
00:04:45,430 --> 00:04:49,965
So a quantum computer sets up some qubits,
applies quantum gates to entangle them

82
00:04:49,965 --> 00:04:53,171
and manipulate probabilities,
then finally measures the outcome,

83
00:04:53,171 --> 00:04:57,501
collapsing superpositions to an
actual sequence of zeros and ones.

84
00:04:57,991 --> 00:05:00,996
What this means is that you
get the entire lot of calculations

85
00:05:00,996 --> 00:05:04,138
that are possible with your setup
all done at the same time.

86
00:05:04,728 --> 00:05:06,895
Ultimately, you can only
measure one of the results,

87
00:05:06,895 --> 00:05:09,466
and it will only probably
be the one you want,

88
00:05:09,466 --> 00:05:11,697
so you may have to
double-check and try again.

89
00:05:12,717 --> 00:05:15,886
But by cleverly exploiting
superposition and entanglement,

90
00:05:15,886 --> 00:05:17,888
this can be exponentially more efficient

91
00:05:17,888 --> 00:05:20,427
than would ever be possible
on a normal computer.

92
00:05:21,747 --> 00:05:25,463
So, while quantum computers will probably
not replace our home computers,

93
00:05:25,463 --> 00:05:28,201
in some areas they are vastly superior.

94
00:05:28,771 --> 00:05:30,457
One of them is database searching.

95
00:05:30,817 --> 00:05:32,264
To find something in a database,

96
00:05:32,264 --> 00:05:35,479
a normal computer may have
to test every single one of its entries.

97
00:05:36,019 --> 00:05:38,812
Quantum algorithms need only
the square root of that time,

98
00:05:38,812 --> 00:05:41,934
which for large databases
is a huge difference.

99
00:05:42,761 --> 00:05:46,595
The most famous use of quantum
computers is ruining IT security.

100
00:05:47,235 --> 00:05:49,746
Right now, your browsing,
email, and banking data

101
00:05:49,746 --> 00:05:53,193
is being kept secure by an encryption
system in which you give everyone

102
00:05:53,193 --> 00:05:56,587
a public key to encode
messages only you can decode.

103
00:05:57,057 --> 00:05:59,889
The problem is that this
public key can actually be used

104
00:05:59,889 --> 00:06:02,014
to calculate your secret private key.

105
00:06:02,544 --> 00:06:05,520
Luckily, doing the necessary math
on any normal computer

106
00:06:05,520 --> 00:06:07,690
would literally take
years of trial and error.

107
00:06:08,110 --> 00:06:10,520
But a quantum computer
with exponential speedup

108
00:06:10,520 --> 00:06:11,906
could do it in a breeze.

109
00:06:12,636 --> 00:06:15,345
Another really exciting
new use is simulations.

110
00:06:15,795 --> 00:06:18,897
Simulations of the quantum world
are very intense on resources,

111
00:06:18,897 --> 00:06:22,062
and even for bigger structures,
such as molecules,

112
00:06:22,062 --> 00:06:23,954
they often lack accuracy.

113
00:06:24,504 --> 00:06:28,254
So why not simulate quantum physics
with actual quantum physics?

114
00:06:29,004 --> 00:06:31,888
Quantum simulations could provide
new insights on proteins

115
00:06:31,888 --> 00:06:33,783
that might revolutionize medicine.

116
00:06:34,403 --> 00:06:36,878
Right now we don’t know
if quantum computers will be

117
00:06:36,878 --> 00:06:40,680
just a very specialized tool
or a big revolution for humanity.

118
00:06:41,090 --> 00:06:43,733
We have no idea where
the limits of technology are,

119
00:06:43,733 --> 00:06:45,863
and there’s only one way to find out!

120
00:06:47,563 --> 00:06:50,625
This video is supported by
the Australian Academy of Science,

121
00:06:50,625 --> 00:06:53,525
which promotes and
supports excellence in science.

122
00:06:54,425 --> 00:06:56,595
Learn more about this topic
and others like it

123
00:06:56,595 --> 00:06:58,567
at .

124
00:06:58,911 --> 00:07:01,917
It was a blast to work with them,
so go check out their site!

125
00:07:02,387 --> 00:07:06,070
Our videos are also made possible
by your support on Patreon.com.

126
00:07:06,630 --> 00:07:10,796
If you want to support us and become part
of the Kurzgesagt bird army,

127
00:07:10,796 --> 00:07:12,361
check out our Patreon page!