This document provides an overview of quantum teleportation and its potential uses and limitations. It discusses how quantum teleportation works through quantum entanglement to instantly transfer information between two locations without the information traveling through space. It describes how quantum teleportation could enable highly secure communication by allowing the generation of encryption keys that would be nearly impossible for an attacker to intercept. However, it also outlines current limitations like low success rates and the difficulty of maintaining entanglement over long distances. The document concludes that while challenges remain, quantum teleportation and computing show promise to revolutionize communication security and computing power in the future.

1. Quantum Teleportation: A Brief Overview of How it Functions and its
Possible Uses
Sean Boland
Abstract— As the conventional means of communication age,
more ways than ever are being found to exploit them. In the
digital world, cryptography continues to become more prevalent
and more widely known, leading toward increasingly larger
numbers of both successful and harmful attacks on ’secure’
information. Such attacks not only call for more research into
the fields of cryptography and security systems, but also into
new ways of communication. With the creation of machines
that can successfully utilize quantum mechanics to teleport
information instantaneously and without leaving a message
to intercept, a new form of highly secure communication is
arriving at exactly the time it is needed. Though there are
limitations due to currently available technology, quantum
teleportation serves as a groundbreaking basis to an important
and advanced technological leap forward.
I. INTRODUCTION
Communication throughout history has always been inter-
ceptable. Ever since humans first thought to keep information
secret, others have strived to discover those secrets. From
eavesdropping to wire-tapping to backdoors that bypass
encryptions, people who steal information have been creating
ever more complicated means to keep up in the figurative
arms race between them and those who create the security
and cryptographic systems themselves.
Before writing, information would either be discussed
in secure locations, or relayed by messengers, and others
who desired to steal the information would eavesdrop on
the party’s conversation or intercept said messenger. After
the creation of formal writing systems, messages could be
sent without their carriers knowing what they contained, but
seeing as these methods were still interceptable, ciphers or
other ways of hiding the information were created. Around
500 BC, Demaratus, a deposed king of Sparta, sent warning
to Greece of an imminent attack from the Persian empire
by writing it in wood and covering the message with wax,
creating a wax tablet with an unimportant correspondence
on the front, as was a common form of communication for
the time. During his time as a Roman general, Julius Caesar
created one of the earliest known ciphers as a way to encrypt
messages to his troops, simply shifting the alphabet by a set
number of letters in order to make the messages unreadable
without sitting down and deciphering them; something a spy
would not have time to do without being noticed[1]
. In more
desperate situations, messages were hidden in public view,
such as certain letters in a public document having been
printed in a different typeface to spell a message, or Jeremiah
Denton blinking in Morse code during a television broadcast
to warn the United States that he and the other captured
soldiers in the Vietnam war were being tortured.
Skipping ahead to the advent of computers and the in-
ternet, because of the nature of the internet, messages and
documents could now be read without the original sender’s
or recipient’s knowledge, and new, more complicated, forms
of cryptography had to be created to secure the data. Key
cryptography is a prevalent form of cryptography originally
conceived in the late 19th century that was adapted and
improved upon for use with computer systems. The basis
of key encryption is that the values of each character in a
message are manipulated in some way by a key to encrypt
the message in such a way that only someone with the same
key (in single-key encryption), or a specific, private key (in
two-key encryption) can decrypt and read the message. This
type of cryptography is used for digital signatures, password
encryption, and end-to-end encryption. The largest current
(external) threats to key-systems are known as man-in-the-
middle attacks[2]
. These are situations in which a third party
impersonates the recipient in some way so that the message
is encrypted with a key known to the attacker, who decrypts
the message, and then re-encrypts it with a key shared with
the real recipient before sending it to them. Because both
the sender and recipient of the messages believe that they
are sending messages to each other, and because they are
both receiving messages as if nothing is wrong, they are
never made aware of the third party whom is also receiving
and decrypting their messages.
Counteracting such man-in-the-middle attacks is where
quantum cryptography, or more specifically, quantum tele-
portation and quantum key-exchanges could revolutionize
communication yet again.
II. EXPLAINING QUANTUM CRYPTOGRAPHY
A. Quantum Teleportation
Quantum teleportation is the instantaneous transfer of
information from one point to another. This differs from
normal forms of information transference or communication
in that the information does not travel from one location to
another, but rather ceases to exist in one location, and springs
into existence in another, set location. This is achieved
through the use of a particle phenomenon known as quantum
entanglement.
Quantum entanglement is a physical phenomenon that
occurs when particles (a pair in this case) are linked in such
a way that the quantum state of one cannot be described
separately from the quantum state of the other and must be
described as if the particles were one and the same, even if
they are separated by huge distances. Once a pair of quantum

2. entangled photons are separated, any change in one will be
instantaneously made in the other as well.
For example, in the “Quantum Teleportation over 100 Km
of Fiber Using Highly Efficient Superconducting Nanowire
Single-photon Detectors” experiment[3]
, the original, entan-
gled photons are created at random to hit the detectors either
one nanosecond early or late, so their states are either ‘early’
or ‘late’, representing the 1’s and 0’s of bits. However,
since in this case it is unknown which state the photons
are in as they are unmeasured, they are considered both. In
a situation which is effectively the quantum equivalent of
Schrodinger’s cat, the very act of measuring the state of a
particle defines the state of that particle. This is known as a
quantum superposition, where the peaks of the states’ waves
can either be in phase, where they line up and multiply each
other, or out of phase, where the waves cancel each other
out. This is a property that is unique to quantum bits, or
‘quibits’ as opposed to conventional, binary bits.
Fig. 1. A visual representation of the experiment, courtesy of Kelly Irvine
and the National Institute of Standards and Technology[4].
The experiment begins by generating a photon of an
unknown state and then splitting it into two photons which
are quantum entangled. The output photon is sent through 60
miles of optical fiber to its destination, while its entangled
photon is sent into a collision with a new input photon of
which the state is known, so it is either early or late. When
the two photons collide, they are both destroyed, but not
before the entangled photon takes on the state opposite to
that of the input photon. Since the entangled photon’s state
was changed, the output photon’s state was also changed at
the exact time the change occurred 60 miles away.
Because the information never traveled through any chan-
nels to show the message at the output photon, methods
such as intercepting the information through surveillance
or wiretap methods along the route of information flow is
impossible. The only way for someone to discover the output
would be to see it at either its origin or destination.
B. Quantum Key-Exchange
Where quantum teleportation truly shines is when it is
added to the traditional key exchange problem, turning it
into the quantum key exchange problem.
To extend the range of communication with quantum
teleportation, waystations or repeaters would have to be
created at distance intervals along the route of communi-
cation. These repeaters would act in much the same way
as conventional repeaters do for boosting cell phone signals
over long distances. One downside that may come to mind
would be that these repeaters create places for a third party to
intercept messages between two people. However, quantum
teleportation thwarts the normal man-in-the-middle attack.
Using the BB84 protocol by Charles H. Bennett and Gilles
Brassard[5][6]
, Alice, the sender, will send Bob, the receiver,
a message consisting of a stream of randomly polarized
photons. A polarized photon is one of the pairs of states
within one of the conjugate state pairs that represent binary
numbers. In figure 2, the states are represented as ↑ = 0, →
= 1 for one conjugate (+), and = 0, = 1 for the other
(x). Bob will then pass Alice’s stream of photons through his
own randomly polarized filter and tell her the polarizations of
the photons that he gets. If the wrong conjugate was chosen
to measure one of the photons in, the result has a 50% chance
to be either arrow in the pair, so Alice will tell him which
arrows (photons) made it through his filter correctly, and the
resulting set of arrows will represent their shared key.
When an eavesdropping third party, Eve, is placed into a
position to intercept Alice’s photon stream to Bob, however,
this changes. Eve must also use a randomly polarized filter
to pass Alice’s photon stream through, but since the photons
were destroyed when she measured them, she must also send
the results she received as a stream of photons to Bob. If she
chooses the wrong filter for any of Alice’s photons and sends
that result to Bob, Bob could choose the same filter that Alice
had, but have a 50% chance to get the wrong arrow, which
is exactly what happens in figure 2.
Fig. 2. A chart showing an example of the BB84 protocol in action, with
Eve in the center, trying to eavesdrop.
In the figure above, there were two instances where Eve
chose the wrong filter and Bob the correct one, in one of
these, Bob received the wrong arrow (photon state), but in
the other, received the correct one by chance. This error in
the results should not have existed, as Bob chose the correct
filter, and there should have been no way for him to receive
the incorrect state. This means that Alice and Bob have been
made aware of Eve’s existence, will not use the created key,

3. and can choose to create a new key later or on a different
channel in order to avoid her.
Because attempting to intercept a quantum key gives Eve
a 50% chance for each filter to be wrong, and Bob a 50%
chance to get the wrong photon state from that filter if he
chooses the correct filter, Eve’s chance of detection is 25%
per photon. This may also be written as a formula:
1 − (3/4)number of photons
So, in attempting to intercept the photon stream from
figure 2, Eve had a 90% chance of being detected, and if
Alice and Bob doubled the number of photons in the stream
to 16, she would have a 99% chance of being detected.
The very nature of quantum teleportation invalidates a
currently successful form of anonymous information gath-
ering almost entirely with just 16 photons. Though a key
of less than or equal length of 16 bits would be easily
crackable through other means if used to encrypt messages
on conventional channels.
III. QUANTUM DECRYPTION
In contemporary cryptology, all key cryptographic systems
are based on the concept of integer factorization being
impossible (or at least infeasible) to solve with contemporary
computer systems for large integers that are the products
of only a few prime numbers such as 300-digit primes[7]
.
Many contemporary cryptographic systems are based on the
complexity of the algorithm that could be used to decrypt
them. For example, though Shor’s algorithm can break an
integer into its prime factors, it is a quantum algorithm, and
subsequently could only run on a quantum computer.
If a quantum computer were used for decryption, however,
it would be able to decode messages, without using a key,
in polynomial time, as well as decode any other systems
based on the difficulty of solving large integers. Such sys-
tems would include email encryption, secure webpages, and
numerous other data types on the internet. Decrypting these
systems would have widespread and problematic implica-
tions for privacy and security on computer systems.
There are types of encryption that currently exist and are
not solvable as of yet through quantum algorithms, however,
and would remain secure even with quantum computers in
use, such as the McEliece cryptosystem[8]
. Also, quantum
cryptography would come into use along with quantum
decryption methods, and would protect even key-encrypted
information from both contemporary and quantum decryp-
tion simply due to the information not existing in any places
beside those of the sender’s and receiver’s computers. It is
also unknown what encryption methods could be created by
utilizing a quantum computer.
IV. LIMITATIONS
Though impressive even as they exist today, quantum tele-
portation, cryptography, and computing unfortunately have
major downsides that keep them from being feasible to use
in present day.
A. Quantum Decoherence
When a quantum system is not kept in perfect isolation
from its surroundings, the process of quantum decoherence
begins, the system’s coherence begins to decay irreversibly,
and the quantum behavior that allows for the system to work
is lost. As decoherence progresses, quantum entanglements
are created between the system and its surroundings, causing
the system to begin to share or transfer its information to
them[9][10]
.
B. Success Rate
Though the 60-mile quantum teleportation experiment[3]
was successful, there were issues with how many times a
set of entangled photons would fail to even survive to the
point of teleportation, as well as how many photons were
actually teleported. According to the researchers themselves,
because of the manner in which the experiment focused on
specific combinations of quantum states, teleportation was
possible, at best, only successful 25% of the time. In the end,
the researchers, teleported 83% of the possible transmissions
successfully, and while it did prove that the teleportation was
indeed quantum-based, that still leaves almost one-fifth of
the currently possible teleportations as lost, which would
be an unreasonable amount for key-exchange or modern
communication systems such as text messaging or email.
“Only about 1 percent of photons make it all the way
through 100 km of fiber.” - Marty Stevens[11]
.
C. Upkeep
Though currently possible, multiple quantum teleportation
repeaters are largely infeasible due to what would be high
upkeep costs. For quantum teleportation to work, supercon-
ductivity is required[3]
. So, quantum repeaters would need
to house large, powerful, energy-draining freezers in order
to keep the superconductive wires at the one-degree above
absolute-zero needed for teleportation to succeed.
V. CURRENT USES
• University of Calgary researchers in Canada have re-
cently successfully used quantum teleportation over 6
kilometers of actual city infrastructure rather than in a
lab setting. They used unused cables under the city of
Calgary to do so[13]
.
• Researches at Google were able to use Google’s Quan-
tum Dream quantum computer to successfully model
and produce the first completely scalable quantum sim-
ulation of a hydrogen molecule. This could lead to more
molecules being modeled, allowing us to better under-
stand particle-level physics, chemistry, and medicine,
leading to breakthroughs in all fields[14]
.
• Some of the information that Edward Snowden leaked
about the NSA in 2014 shows that the agency was
attempting to build “a cryptologically useful quantum
computer” for cracking most contemporary encryption
types. According to documents given the Washington
Post, the computer was and possibly still is ”part of a

4. $79.7 million research program titled ‘Penetrating Hard
Targets.’”[15]
• In August, China successfully launched the first ever
quantum satellite into space. The satellite was created
“to establish ultra-secure quantum communications” by
using quantum teleportation to transmit complex cryp-
tographic keys between Earth and space, as well as
investigate quantum phenomena[16]
.
VI. CONCLUSIONS
Despite current limitations due to modern technology,
quantum teleportation, cryptography, and computers only
stand to improve in the coming years. As of today, quantum
teleportation has been proven both possible and feasible in
urban environments as well as labs, quantum cryptography
is able to create traditionally undecryptable means of digital
communication, and quantum computers have grown to the
point of being able to map the building blocks of matter
itself. Even with some justified reasons for concern in the
field of cryptology, quantum computers will prove only to
advance the field once the transition period is over. As the
field of quantum computing theory continues to grow, it will
both benefit and forever change all fields of science, not just
computer science.
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