The Quantum Internet: Hype or the Next Step

Quantum Internet/John Ashmead October 2nd, 2021 Capclave http://timeandquantummechanics.com
Quantum Internet:
Hype? OR the next Step?
• What is the quantum internet?
• Why do we need more than just quantum
computing?
• What are quantum cryptography, quantum
key distribution, quantum sensors;…
• How are these ideas entangled?
• Is it just that each has quantum in its name?
• Or is the whole more than the sum of the parts?

Overview
• Quantum Mechanics
• Quantum Computing
• Quantum Internet
• Hype?
• Or the next logical
step?
• We reflect on the
situation

Spooky action at a
distance
• EPR 1935
• Two particles with
a common origin,
entangled
• Measure one &
you have
measured the
other
• Which seems
strange

Bertlmann’s socks
• Pink or non-
pink
• Secrets of the
successful sock
planner
• Can we explain
spooky socks?

Bell’s theorem
• Many angles
• Different
correlations
• All must
match
• But there is
NO way

FLASH
A Superluminal Communicator
Nick Herbert
• See if we can use EPR to
send information
“Faster-than-light”
• Which means
“backwards-in-time”!
• Alice does vertical or
circular measurement
• Bob sees if he see which
kind of measurement
she did

No cloning Theorem
• From “Mirror, Mirror”
• We do not duplicate either
Kirk or Mirror-Kirk, we
interchange them
• No cloning theorem says we
can’t copy
• Invented by Wooters & Zurek
a few months after Herbert’s
Flash
• There is a no-deleting theorem
as well

Qubits — Electron
Spin
• Archetypal qubit
• Usually we are most
interesting in the up & down
states (z direction)
• But can point in any direction
• Pure states: arrow gets all the
way to the sphere

Photonic Qubits
• Electrons not as practical as
photons
• So can use the polarization
directions of the photon as
well
• So we can look at the photons
in horizontal & vertical
• Or 45 & -45 degrees
• Or clockwise & counter-
clockwise …

Quantum Gates
• Bit gates are
foundation of
classical computers
• One qubit gates: flip
& rotate.
• Controlled NOT
(shown)
• Like a quantum
faucet
• Lots of other possible
gates as well
If first qubit is up,
leave the 2nd qubit alone
If first qubit is down,
flip the 2nd qubit

Quantum circuits
• Codeproject:
Quantum-
Computation-Primer
• The H is the
Hadamard gate
• The ellipse is C-Not
or Controlled Not
gate
• X, Z are simple
rotations around the
x, z axes
• …

Shor’s algorithm
• 1994 breakthrough
• Basically a quantum
Fourier transform
• Plus a lot of wrapper
stuff
• Very ingenious!
• Youtube:
minutephysics Shor’s
Algorithm

Error correcting
codes
• Triplicate the original
state
• Can fix without
“measuring”
• Aligns 2 up & 1
down to 3 up
• Aligns 2 down & 1
up to 3 down
• Taminiau, 2014, for
“diamond memory”

Shor breaks the
Internet
• Quantum computers can
do operations in parallel
in a way that classical
computers can not
• One extra qubit on a
quantum computer is the
same as doubling the
size of a classical
computer
• So that things — like
breaking RSA encryption
— that could have taken
“age of universe” can
now take seconds.

Quantum internet
• Quantum supremacy
• Quantum cryptography
• Quantum teleportation
• Quantum memory
• Quantum sensors

https://phys.org/news/2020-08-google-largest-chemical-simulation-quantum.html
• One of the most
important problems for
QC
• Suggested by Feynman
• Google QC “Sycamore”
did in 200 seconds what
IBM’s supercomputer
“Summit” would need
10,000 years to do.
• IBM says only 2.5 days,
so take that!

Random Keys
• One time
pads
• Either
photon goes
one way or
the other
• As random
as a Geiger
counter

Quantum keys
without distribution
• Artur Ekert 1991
• Keys created by measurement
• Alice & Bob randomly measure
in H/V directions
• They compare their settings &
discard all inharmonious bits
• Use 1/2 of the remaining bits
to check Bell’s theorem. If
violated, then there is an
eavesdropper
• Other half are the key

Quantum
Teleportation
• transports the full quantum
state
• but needs a classical channel to
define it on the far side

• OK, problem “solved”
• A network of trust? Doesn’t
that, like, defeat the point?
Quantum repeaters

Quantum storage
• How to remember without
measuring?
• Note human memory uses a
store, retrieve, store back model
• The NV center's electron spin,
localized at atomic scales, can
be manipulated at room
temperature by external factors
such as magnetic, or electric
fields, microwave radiation, or
light, resulting in sharp
resonances in the intensity of
the photoluminescence.

Quantum
Sensors • LIGO - gravitational
wave detectors
• Had been using
classical
interference to spot
gravitation waves
• But switched to
using quantum
“squeezed states”
• Got factor of 2
improvement in
sensitivity
https://physics.aps.org/articles/v12/139

https://q2b.qcware.com
• Current directions
• Scalability
• Error correction
• Algorithms
• Business uses
Where are we
headed?

Will we ever have a
quantum computer?
• Quantum systems extremely
vulnerable to errors
• A really clever error correction
algorithm using qubits doesn’t
help if you can’t keep your
qubits stable
• With the quantum supremacy
thing, they could have done it
even faster but qubit #54 failed.
• That’s at temperatures of milli-
Kelvins. Outer space is
thousands of times warmer
than that!

So factoring all this
in …
15=3*5
21=3*7
35=?*?
• how to factor 15?

High quality photons
• Generates high quality single
photons on a chip
• Chip is built with conventional
facilities
• Useful for quantum
computing & communication
• But probably for lots of other
stuff as well
https://phys.org/news/2020-05-photon-discovery-major-large-scale-quantum.html

Measurements
• Stern-Gerlach
experiment
• Should be
continuous
• But is discrete
• Hunh?
• Checkpoint
Copenhagen

The Collapse of the Collapse
of the Wave function
• System & detector weakly
coupled
• At the start, the impact of the
system on the detector is fuzzy
• Over time, it gets sharper with
more definition
• Until we now see definite
quanta!

• Quantum mechanics predicts a
number of, at first sight,
counterintuitive phenomena.
• It therefore remains a question
whether our intuition is the best
way to find new experiments.
• computer algorithm MELVIN
which is able to find new
experimental implementations
for the creation and
manipulation of complex
quantum states.

Quantum Internet:
Hype AND the next step!
• Right now, pretty serious level
of hype
• But clear step-by-step progress
• And some real
accomplishments
• Both directly & in terms of
understanding
• While quantum internet
provides useful set of targets:
memory, repeaters, & so on

References
• Lloyd — Programming the
Universe
• Dowling — Schrödinger’s
Killer App
• Dowling — Schrödinger’s Web
• Fürnkranz — Quantum
Internet: Ultrafast & Safe from
Hackers
• Jaeger — Second Quantum
Revolution

The Quantum Internet: Hype or the Next Step

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