Defense Intelligence Reference Document Quantum Computing And Utilizing Organic Molecules In Automation Technology

UNCLASSIFIED//POI\ GI I ICIAL USE 014Jtf
APPLICATIONS OF QUANTUM COMPUTERS
Although smaller circuitry and supercomputing is a motivator, the driving application behind
quantum computing is cryptography. First, there is cracking cipher codes. The vast majority
of secured communications utilize a method known as public-key cryptography. In this
method, the code is based on the prime number factors of a very large integer which is
publically available. The private key is one of the integer factors and this allows the receiver
of information to decipher the code easily. The strength of this technique is that traditional
computer algorithms will take a long time to guess the correct factors of the public key, on
the order of months.9 Traditional brute force methods require a number of steps that
increase as an exponential function of the size of the public key. However, in 1994 Shor
presented a quantum algorithm that would only require a polynomial number of steps, thus
dramatically decreasing the required time to factor, assuming a quantum computer would
ever be physically realized. (6) This speedup is primarily due to the nature of quantum
waves; specifically, they can follow several parallel paths instead of the usual stepwise
procedural execution of instructions. This acceleration by superposition concept is more
easily understood in a random search of data. Consider an algorithm that has a 50%
probability to locate a specific phone number in a database of N phone numbers by a random
search. The procedural algorithm on average will require O.SN inquiries to locate the correct
number. A quantum algorithm on the other hand can be devised that accumulates
information by examining multiple numbers with each step. Such a scheme has been shown
to reduce the number of examinations required to ✓N. (7, 8) The superposition of states
allows examination and processing of several tape cells simultaneously in a Turing-inspired
machine.
Second, there is quantum communication. Once public key encryption is easily broken by the
quantum computer, a new cipher needs to replace it. The canonical quantum communication
experiment defines a sender, Bob, and a receiver, Alice. In most scenarios, Alice and Bob
communicate over a distance using entangled particles and a traditional open line. The open
line relays information about measurement settings, but is useless to an observer without
access to the entangled wave function (entanglement is discussed below, and the open line
information is an analogue to the public key of current ciphers). The other advantage of this
setup is that almost any disturbance in the communication line between Alice and Bob would
destroy entanglement and thus the information would be lost instead of intercepted.
Additional archetypical participants in a communications experiment/scenario follow the
English alphabet: Charlie (or Chuck if his intent is malicious), Dave, Eve, etc. Quantum
communication is thus an application replacing one performed by a general purpose
computing machine; the classical and quantum systems do not operate in similar fashion
other than the function of securely transmitting information. Additionally, quantum
communication has been suggested as a method to connect isolated quantum systems
without disturbing closed box requirements like classical interventions would. (9, 10)
Beyond cryptography is a third application, quantum metrology, where time and/or distance
are measured to an extremely high accuracy. A fourth obvious application is simulation of
quantum systems. (11, 12)
g Or hours if one has farms of supercomputers. The point is that the value of most communication is much smaller than
the cost to decipher by brute force. The 128-bit web standard is a compromise between security and speed.
10
UNCLASSIFIED/;'f8R: 8ffl@IJliL ~81!! 8HLY