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Quantum Computation and Communication

The amazing world of quantum mechanics may revolutionize the way logisticians compute support requirements and communicate on the battlefield.

Editor’s note: Innovative developments in science and technology will change how the Army is deployed and sustained. This is the first in a series of articles written by members of the Army Logistics Innovation Agency’s Futures Group that survey some of the most promising possibilities.

We live in a time of unprecedented technological advances that hold profound logistics implications for our Army. The journey to fascinating, powerful, and novel computation and communication capabilities, in particular, will lead to new scientific and technological developments with many benefits to Army logistics.

“Quantum Computation and Communication” is one of five themes for future logistics innovation identified by the Army Logistics Innovation Agency (LIA) at Fort Belvoir, Virginia. The others are “Prediction and Cooperation,” “Energy-on-Demand,” “Designer Materials,” and “Telepresence.” Each of these themes describes plausible future advances in technology and business processes that may improve logistics effectiveness significantly. They also depict future conditions under which logistics functions will be significantly improved and logistics requirements radically reduced. Together, the themes offer an advanced look at some amazing possibilities for Army logistics.

Our goal in this and subsequent articles in Army Logistician is to explain the science underlying these themes in plain language while outlining the possibilities they offer for future logistics. In this article, we examine the salient features of quantum computation and quantum communication. We will explore the quantum world and explain how quantum mechanics (QM) forms the bedrock of these emerging technologies. The effects of QM are counterintuitive and require that we rethink our everyday view of how the world operates. Relating the effects of QM to quantum computation and quantum communication will give you an appreciation of how these technologies will benefit and revolutionize logistics. Admittedly, this is a challenging subject. The terminology and concepts will be new to many readers. But we feel it is important to realize that, over the course of a 20-year career, today’s sergeants and second lieutenants undoubtedly will be affected by developments in this and related scientific fields.

We should mention that LTA serves a unique role in the Army logistics community. As “scouts” for advanced business processes and technology for the Army’s Deputy Chief of Staff, G–4, LTA looks for opportunities to inform the logistics community about research efforts of potential value to logisticians. Articles like this provide information that can contribute to the development of a vision for future logistics capabilities, policies, and plans.

Technology for a New Logistics Environment

Future Army logisticians will have to manage a range of logistics functions across an end-to-end logistics enterprise and will need tools that permit effective decisionmaking and rapid, dynamic planning.

In an increasingly complex environment, we must consider new ways to model and analyze diverse and dynamic processes that exist at globally distributed locations. We must be open to the most efficient methods of modeling interrelated phenomena among the intelligence, operational, and logistics domains. Decreased cycle time, increased situational awareness, and secure transmission of real-time logistics information are just some of the benefits that quantum computation and quantum communication will offer to Army logistics. These exciting new fields of science will harness the fundamental laws of physics to dramatically improve the acquisition, transmission, and processing of logistics information. The goal is unprecedented computation capabilities and secure communications for complete battlefield dominance.

Emerging joint warfighting concepts require that Army logisticians be completely integrated into the joint fight. To realize fully many of the capabilities prescribed in the Joint Logistics (Distribution) Joint Integrating Concept, Army logisticians must perform their missions with unprecedented levels of connectivity and joint interdependence. Quantum computation and quantum communication promise to provide those capabilities. Quantum computers would be capable of computing at speeds far exceeding those of conventional computers and performing calculations that are too large for conventional computers to complete in a reasonable time. Likewise, quantum communication devices would allow for real-time, highly secure transfer of information with near-zero latency. [“Latency” refers to the time lag encountered in an end-to-end communication. Humans can detect time lags of about 16 milliseconds and greater. “Near-zero latency” refers to a lag of less than 16 milliseconds.]

The Quantum World

Before 1900, the laws of classical physics did an excellent job of describing large, slow-moving particles, but they could not explain the behavior of subatomic particles such as electrons, protons, neutrons, photons, and quarks. It was not until the development of QM that the behavior of such particles could be explained.

Today, QM is the most satisfactory theory available for explaining life in the quantum world. QM, however, is notoriously difficult to understand because it requires a complete revision in our concept of a “particle.” While the features of QM presented here may seem bizarre, it is important to remember that a host of astonishing, practical applications have resulted from QM. Some everyday examples include the laser, the processors in a computer, and the many forms of medical imaging in use today. With this in mind, let’s try to understand those features of QM that are most relevant to quantum computation and quantum communication.

What is a subatomic particle? The development of QM followed a number of surprising observations that could not be explained by classical physics. One observation in particularthe photoelectric effectled Albert Einstein to suggest that light exists in discrete packets of energy called “photons.” Before 1900, light always was described as a wave. After Einstein, light was described as consisting of little “quanta” of energy. Today, physicists accept the fact that light behaves as both a wave and a particle—it has “wave-particle duality.” In fact, it is the wave-particle duality of light that allows night-vision goggles to operate. Light exhibits wave-like properties when passing through the goggles’ lens but particle-like properties when it hits the goggles’ internal sensor.

In the years following Einstein’s suggestion, suitably designed experiments demonstrated that electrons also exhibit wave-particle duality. At the time, QM’s proposition that electrons had wave-particle duality was quite disconcerting. Didn’t electrons have mass? Weren’t they little point-like things that orbit the nucleus of an atom like planets orbiting the sun? Perhaps even more disconcerting was the fact that wave-particle duality applies to all subatomic particles. Quantum particles were not the tangible particles that we were used to. QM rendered our conventional images of particles obsolete.

Where is that particle? If a subatomic particle is not really a particle in the classical sense, then how can we say where it is? In QM, the physical properties of subatomic particles are not evident until someone decides to measure them. This is rather disquieting. It implies that physicists can predict the possible outcome of a particular measurement but cannot, with absolute certainty, ensure the outcome of that measurement.

The definite location of an electron, for example, cannot be given until one measures its location. Before a measurement is made, the particle is actually in several possible locations, so several possible outcomes to its whereabouts are possible and the best one can do is give the probability that it will be “over here” or “over there.” In the language of QM, the particle is said to be in a “superposition of states.”

Immediately after a measurement is made, we can say with certainty where the particle is; but until the particle is measured, it does not have a position. This feature of QM is very important to both quantum computation and communication. As we will see shortly, the fact that measuring a subatomic particle forces it to take a value is the feature that allows us to know if a quantum communication has been compromised.

Where is that particle going? Isaac Newton is famous for, among other things, the laws of motion governing everyday objects. For example, given the position and momentum of an object, we can determine where that object is going using Newton’s laws of motion. In QM, the position and momentum of a subatomic particle cannot be measured with very high accuracy. Simply trying to measure the position of an electron will alter its state. If we measure its position with great accuracy, we alter its momentum; if we measure its momentum with great accuracy, we alter its position. These features are embodied in what is called the “Heisenberg Uncertainty Principle.” This principle, along with wave-particle duality and super-position of states, is crucial to our discussion of quantum computation and communication.

Quantum entanglement. Quantum entanglement is actually a useful feature of QM; it is a resource at our disposal. To explain what it is, suppose that we have two photons that have become interrelated. If a measurement of one photon instantly influences the other photoneven if the photons are very far apart and isolated from each otherthen these two photons are “entangled.”

As an example, let’s introduce two characters, Alice and Bob. When photons travel, they vibrate, and the direction in which they vibrate is called “polarization.” (See figure A above) Now, let’s consider that Alice and Bob share entangled (and perfectly correlated) polarized photons. Alice (let’s put her on Earth) has one photon, and Bob (let’s put him on the Moon) has the other photon. It is important to realize that, while these entangled photons are polarized, neither Alice nor Bob knows what the polarizations are. If Alice then proceeds to measure the polarization of her photon with a polarizer and finds that it is vertically polarized, then Bob’s photon must be horizontally polarized. (See figure B above.) Such quantum entanglement, which Einstein called “spooky,” is of fundamental importance for quantum communication and, in particular, for quantum teleportation.

The main characters. The stage is now set. Quantization (subdivision into quantum particles), wave-particle duality, superposition of states, uncertainty, and entanglement are the only features of QM that we need to consider in order to explore quantum computation and communication. It is important to realize that these quantum effects are not a result of shortcomings in QM but that they are inherent in nature; they reflect the essence of our world.

Quantum Computation

We begin our discussion of quantum computation with an example adapted from Dr. Lov Kumar Grover, the inventor of the Grover quantum search algorithm.

Assume that you are trying to solve a crossword puzzle and you have the following: _ _ r _ n h _. (The solution is “piranha.”) In an effort to solve the puzzle, you check an online dictionary with 1,000,000 alphabetically arranged words and then develop a program to search the dictionary automatically for a fit to the puzzle. Your program typically solves the puzzle after looking through 500,000 words. This is really the best one can do using a conventional computer [a computer that measures data in bits (0s and 1s)].

What would happen if we used the multiple states available to a photon or other quantum particle rather than the 0s and 1s of a conventional computer? What if we used a quantum computer (a computer with data that can be in multiple states at the same time)? If we had a quantum computer with an online dictionary, it would be possible to carry out multiple computations simultaneously. A quantum computer, using quantum search algorithms, could complete the search for an answer to our puzzle after 1,000 words.

In the future, database searches will occur at speeds faster than possible with even the most powerful conventional computer in existence today. This kind of revolutionary computing power would be a tremendous aid to the exploitation of massive supply, maintenance, and transportation databases and holds great potential for improving the responsiveness of highly complex logistics systems. So, how does a quantum computer work?

Superposition of states at work. Recall that subatomic particles, until measured, are in a superposition of states. Let’s see how this applies to quantum computation. The memory in a conventional computer is made up of bits. A bit is a binary digit. For example, the binary number 1001011 is 7 bits long. (A byte is a collection of bitsalmost always 8 bits.) A bit can be either a 0 or a 1 but not both. A bit is like a switch; it can either be “on” or “off.” A conventional computer can do three things: it can set a bit to 0, it can set a bit to 1, or it can look at a bit and use it to decide what value to give to some other bit. In a nutshell, a conventional computer operates by interpreting bits and figuring out what to do with them.

A quantum computer uses qubits (quantum bits.) Quantum computers operate by observing the state of qubits. A qubit can be a 0, a 1, a combination of the two, or it can represent a number that is somewhere between 0 and 1; that is, it can be in a superposition of states. Now, imagine for a moment that you have 200 qubits; this represents a quantum superposition of as many as 2200 states. Each one of these states is equivalent to a conventional computer’s single list of 200 1s and 0s. A quantum computer would simultaneously operate on all 2200 states in the process of doing a computation. In the same amount of time it takes a conventional computer to operate on one state, a quantum computer can operate on 2200 states.

To perform a calculation in the same amount of time as a quantum computer, a conventional computer would need 1060 processors. This amount of computing power is staggering; we certainly would not use such a computer for word-processing or email. Dr. Peter W. Shor of AT&T’s Bell Laboratories has provided an application of a quantum computer, rapidly factoring very large numbers in a matter of seconds. Currently, the premier application of quantum computing is in the area of cryptology, which is the art of making and breaking ciphers (secret codes) that are used to encrypt messages. Virtually all encryption methods in use today can be decrypted using quantum algorithms. However, many exciting potential applications of quantum computers remain to be discovered.

The state of quantum computation today. Current quantum computers can perform simple operations on 2 and 3 qubits. This level of computational power, however, does not rival the conventional computer. The challenges to creating a quantum computer of any value are primarily in the areas of “decoherence” and error correction.

If a qubit comes into contact with its environment (for example, becomes entangled), then its quantum state will decay into a mixed state and the qubit is said to “decohere.” Decoherence destroys the efficiency of a quantum computer. This interaction of quantum states of a particle with the environment is typically referred to as “noise.” Conventional computers correct for noise through error correction codes that store the bits with redundancy (the bits are copied and later recovered). The states of a quantum particle cannot be copied, and, even if they could, we would not know if an error occurred without making a measurement (which we cannot do without altering the state of the particle). Nevertheless, enough progress is being made in error correction so that we can realistically predict (although it is a precarious endeavor to predict technology breakthroughs) that, within a decade, error-free quantum computation on a small scale will be achieved.

Quantum Communication

Quantum communication aims to provide secure communication mechanisms by using the features of QM. Some questions that quantum communication seeks to answer are: What novel ways are there to achieve secret communications? Is it possible to improve the efficiency of sending conventional communications? Is it possible to communicate information to distant locations without ever transporting the actual information? These questions are best answered within the realms of quantum teleportation and quantum cryptography, which are subsets of quantum communication.

Quantum Teleportation

According to classical physics, teleportation is defined as “the disembodied transport of matter through space.” It is perhaps unrealistic to think that an object can be disintegrated in one place, transmitted, and then perfectly reconstructed in another place; the process of teleportation conjures up memories of the “transporter” in the television series Star Trek. QM, however, makes teleportation, in a sense, plausible.

Let’s take this periodical as an example. At the fundamental level, Army Logistician consists of particles such as electrons. According to QM, all “fundamental” particles of the same kind are identical. The electrons in this periodical are identical to the electrons in any other periodical. What are not identical, and what distinguishes this issue of Army Logistician from another magazine, in terms of QM, are the quantum states of the electrons that collectively make up each periodical. QM implies that, to transport matter from one location to another, it is not necessary to actually transport the particles that make up the matter in question. It is sufficient to recreate, in the other location, the quantum states of all the particles that make up the piece of matter. So, teleporting the quantum states of all the particles that make up this periodical would create a replica in another location. In other words, this Army Logistician would have been teleported to the other location.

However, to re-create the quantum state of a particle, one has to measure the particle’s quantum state with great accuracy. We know from our earlier discussion that this is not possible; nature simply will not allow it (recall the Heisenberg Uncertainty Principle). Even if it were possible, re-creating the quantum states of the particles that make up Army Logistician would require a phenomenal amount of informationso much information that it would take much longer to transmit the information than to physically send the periodical by airmail to the remote location in question.

Let’s imagine for the moment that we can determine the quantum state of a particle without measuring it. This is possible if we use entangled pairs of particles. (See chart above.) Let’s assume, again, that Alice and Bob share entangled polarized photons (Alice has photon 1 and Bob has photon 2) and that neither Alice nor Bob knows what those polarizations are. Alice also has another photon (let’s call this photon 3) with an unknown polarization that she would like to teleport to Bob. Remember, Alice cannot measure the polarization of her photons. If she does, she will cause them to assume specific polarizations. But if Alice performs a measurement on her photons jointly, then she will cause Bob’s photon to correlate with the joint measurement she makes. Bob’s photon then will be in the same quantum state (that is, have the same polarization) as Alice’s photon 3. In other words, the state of Alice’s photon 3 will have been teleported to Bob’s photon 2.

Some comments are in order. First, teleporting the state of a photon is completely equivalent to teleporting a photon. Thus, entanglement provides a means of communication. Second, during the process of Alice’s measurement of photon 3 (in conjunction with photon 1), photon 3 became entangled with photon 1 and, as a result, photon 3 lost its original state. In a sense, it forgot what state it was in. This does not matter too much to Alice since she succeeded in teleporting the state of photon 3 to Bob. However, it is important to understand that, if we try to teleport an object from one location to another, the state of the original object will be destroyed in the process.

Classical Cryptography

Cryptography is the art of sending messages in disguised form. Message encryption is accomplished using an “encryption algorithm,” or “key.” Some of the earliest keys in existence consisted of what are known as substitution algorithms. The Caesar Cipher (allegedly used by Julius Caesar), which consisted of encrypting a message by shifting letters, is an example of a substitution algorithm. The size of the shift is the key, and that is what needs to be kept secret. This is where the problem of key distribution arises. The key must be shared between the sender and the receiver in order for the receiver to decipher the message. How can Alice send the key to Bob without an eavesdropper (Eve) monitoring the communication? Without a key, a classically encrypted message must be decrypted using cryptanalysis.

Today, the problem of key distribution is solved and cryptosystems are nearly impossible to crack with conventional computers. The reason is simple: while it is fairly easy to multiply two large numbers, it is very difficult to factor very large numbers because factoring a large number requires a lot of computing power. Our discussion of quantum computation, however, indicates that this might not always be the case. Is there a better way to encrypt messages? Is there a way for Alice and Bob to communicate and know if their communication has been compromised? Classical cryptography has no way of addressing these questions.

Quantum Cryptography: Secure Tansmission

Quantum cryptography is a means of communicating securely using physical objects such as photons. One of the central issues in cryptography, as we have noted, is key distribution. Using mathematics in classical cryptography circumvents the problem of key distribution, but the coming of quantum computers puts classical cryptography in jeopardy. Another way to circumvent the key distribution problem is to use the effects of QM to create quantum cryptography. In quantum cryptography, the security of a communication is guaranteed by the uncertainty principle and by the fact that performing a measurement on a quantum particle alters its state. One way to achieve quantum key distribution is to use polarized photons: bits of information are encoded using polarization.

To demonstrate communication using polarized photons, let’s turn to Alice and Bob again. Alice wants to send an encrypted message consisting of 0s and 1s to Bob and, at the same time, wants to outwit Eve. (See chart below.) She can use a scheme (Scheme symbol 1) in which she represents a 0 with a horizontal photon “—” and a 1 with a vertical photon “|,” or she can use a scheme (Scheme symbol 2) where she represents a 0 with “\” and a 1 with “/.” To send a binary message, Alice sends an unpredictable series of polarized photons using either the Scheme symbol 1 scheme or the Scheme symbol 2 scheme.

In order to intercept the message, Eve needs to identify the polarization of each photon. As she sees a photon coming, she will orient her Polaroid filter. However, every time she performs the wrong measurement, she alters the photon’s state. Alice, after sending her photons to Bob, picks up the phone and tells Bob what scheme she used but not the polarization she used for each photon. In this way, Alice and Bob can monitor the communication for disturbances and will be able to determine if eavesdropping occurred. Bob also will know which photons he measured correctly simply by knowing the scheme that Alice used. In this way, they will have created a secure key that they can use to encrypt further messages. Eve cannot intercept a photon, and she cannot measure the quantum state of that photon with great accuracy and then re-emit it without introducing some error into the communication.

The uncertainty principle guarantees secure communication between two parties. Today, there are point-to-point commercial quantum cryptography devices on the market. Cost, the lack of dedicated fiberoptic lines (for sending the photons), and the nonexistence of single-photon sources are the factors currently limiting quantum cryptography. The use of quantum cryptography over networks is anticipated in the next few years, and long-haul secure quantum communication (such as by satellite optical communications) is anticipated to occur within the next decade.

The range and reliability of quantum cryptography devices currently are a concern. Scientists and engineers may be able to overcome these problems by using devices such as quantum repeaters and by employing quantum error-correction techniques. These devices would enable quantum signals to be restored at distant locations without reading, and hence altering, the quantum information. Quantum cryptography may be applied to achieve completely secure communications involving sensitive logistics plans in support of widely distributed, and, in some cases, potentially vulnerable forces on future nonlinear battlefields.

Future Benefits for Army Logistics

Assuming that scientists can overcome several of the challenges described in this article, it is possible that, within the next decade, we will be able to identify a number of practical applications for Army logistics planners. For example, breaking through the scalability barrier (that is, solving the problem of decoherence) may lead to applications with tremendous military utility for solving seemingly impossible problems inherent in complex systems and chaotic environments. Quantum computation and quantum communication would permit precise logistics support to future Army forces and allow for an enormously high level of control over an integrated deployment, distribution, and sustainment system, so that Soldiers deployed anywhere on the globe would receive exactly the right support at the right time and at the right place.

The future battlespace will be populated by an increasing number of unmanned or robotic systems and equipment, which will place enormous demands on logisticians and their planning systems. In such an environment, with apparently intractable problem sets, quantum computation and communication may serve as enabling technologies for other remarkable future capabilities. In our next article, for instance, we will describe the idea of telepresence (remote presence in the battlespace). In the area of telepresence, there may be a role for emerging quantum technologies such as quantum robots. Such robots, operating within a distributed quantum computing system, could allow small-scale sensors and actuators to be controlled remotely over great distances. This would truly revolutionize the concept of “sense and respond” logistics.

In fact, the speed of quantum computation, properly harnessed, may enable future logisticians to meet, or preempt, real-time requirements rapidly. Rather than relying on logistics estimates that are based on historical data processed at today’s speeds, computational and communication speeds attained from quantum systems may replace “best guesses” with real-time, actionable knowledge. Functioning within a common logistics operating environment, such radically capable systems truly would change the conduct of warfare.

The goal is to remain alert to the advances in quantum information science so that we are better prepared to exploit potential capabilities to solve intractable computational challenges impacting Army logistics. In particular, we are concerned with the application of these capabilities to solve increasingly dynamic logistics planning and simulation requirements. As we monitor advances, we may indeed see new classes of simulations that allow for accurately predicting logistics requirements and outcomes.

We hope that this article and the others that follow in Army Logistician will give logisticians and acquisition personnel a basic understanding of the possibilities, and the limitations, of emerging scientific areas. The intent is to pique interest among the logistics community and allow a glimpse of future concepts and technologies that young logisticians will inevitably encounter in their careers. The Quantum Computation and Communication theme is perhaps the most difficult to grasp conceptually and technically. Subsequent articles will be less complex, but the ideas and scientific areas discussed will be just as significant in their far-reaching implications. The next two articles in this series will address the themes of Telepresence and Designer Materials. Like the other themes, they offer the potential of improved capabilities for deployment and sustainment and a wide range of prospective solutions to the challenges facing logisticians.

Dr. Keith Aliberti is a research physicist in the Sensors and Electron Devices Directorate at the Army Research Laboratory at Adelphi, Maryland. He currently serves as the laboratory’s liaison officer to the Army Logistics Innovation Agency at Fort Belvoir, Virginia. He has a B.S. degree in physics from Rensselaer Polytechnic Institute and M.S. and Ph.D. degrees from the State University of New York at Albany.

Thomas L. Bruen is a logistics management specialist at the Army Logistics Innovation Agency at Fort Belvoir, Virginia. He has a bachelor’s degree in engineering from the U.S. Military Academy and is a graduate of the Army Management Staff College’s Sustaining Base Leadership Management Program.