The Air Force Research Laboratory leads the discovery, development, and integration of affordable war fighting technologies for our air and space forces. In particular, the Information Directorate’s mission is to advance and apply Information Systems Science and Technology to provide Information Dominance. This paper discusses why the Air Force Research Laboratory Information Directorate is concerned with researching prospective computing architectures for Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance applications. Projects addressing quantum information science and quantum computing will be discussed, highlighting where these technologies offer potential disruptive technology solutions for the Air Force.

Light pulses used in quantum key distribution (QKD) designed for polarization entanglement also exhibit frequency entanglement. Although absent from the simplified models that initiated QKD, the degree of frequency entanglement of polarization-entangled light pulses is shown to affect the amount of key that can be distilled from raw light signals. In one example, extreme frequency entanglement generates 4/3 of the amount of distilled key as does no frequency entanglement.

A recently introduced class of sets of maximally entangled quantum states generalizing the Bell basis and called the “Bell gems,” obtained by maintaining of symmetries of the Bell states under changes of scale, are shown to contain a hierarchy of concatenated quantum codes.

In this paper, we consider a natural generalisation of classical proportional navigation guidance for quantum information processing devices. We demonstrate how standard guidance laws can be modified to allow the efficient control of the quantum state of an example qubit. We consider an example experimental system: a Josephson charge qubit (Cooper pair box). The quantum guidance algorithm is assessed in an open-loop control system based on the standard bias fields present in the device, without the need for any additional external fields (such as microwave 'pump' fields, which are often used to drive these charge devices into excited states).

We propose a point to point quantum channel based on a two-color Spontaneous Parametric Down Conversion (SPDC), that may be applied for a Quantum Key Distribution (QKD) system to gain better security. We use one arm of the SPDC (770 nm - optimal for Si detection) and a Si counter at Alice's side to count the exact number of photons in each pulse. Whenever the arm contains exactly one photon, the correlated photon (1550nm - optimal for fiber transmission) in the other arm is sent via a fiber to Bob. In the experiment we used an Ar^{+} laser of 514.5nm wavelength and a BBO crystal to produce type-I photon pairs. We measured the spectrum of the SPDC and resolved specifically the 770 nm wavelength. The rate of correlated pairs (at 890-1050 nm) from our SPDC source was compared to a non-correlated source. We further developed an InGaAs single photon detector based on Geiger mode APD and achieved 10% quantum efficiency and 5 * 10^{-3} dark counts per 20nsec pulse at a temperature of -35 degrees Celsius.

We propose a scalable method for implementing linear optics quantum computation using the "linked-state" approach. Our method avoids the two-dimensional spread of errors occurring in the preparation of the linked-state. Consequently, a proof is given for the scalability of this modified linked-state model, and an exact expression for the efficiency of the method is obtained. Moreover, a considerable improvement in the efficiency is achieved. The proposed method is applicable to the "cluster-state" approach as well.

The spin of an electron confined into a lateral semiconductor quantum dot has been proposed as a possible physical realization of a qubit. While the spin has the advantage of large decoherence times, operations with more than one qubit will necessarily involve orbital degrees of freedom, namely, charge, which is much more prone to decoherence. There are also alternative quantum dot qubit proposals that are entirely based on charge. We have used a realistic model to quantify the limitations imposed by acoustic phonons on the operation of quantum dot-based qubits. Our treatment includes essential aspects of the setup geometry, wave function profile and materials characteristics. The time dependence of the qubit density matrix is the presence of a phonon bath solved within the Born-Markov approximation. We find that the inclusion of geometric form factors makes the phonon-induced decoherence rates in double dot charge qubits nearly one order of magnitude lower than estimates previously in the literature. Moreover, our theoretical prediction for the quality factor of coherent charge oscillations based on phonon decoherence are higher than the values recently observed experimentally. This allows us to conclude that phonons are not the primary source of decoherence in double quantum dot qubits.

To a large extent, the power of a quantum computer comes from the possibility of operating on a number of quantum memories simultaneously. For example, if there are n linearly independent quantum states in each of N quantum memories, then the number of linearly independent quantum states is n^N when they are taken together. This exponential increase is the basis of the present interest in quantum computing. In the context of quantum mechanics as described by the Schrodinger equation (which is a partial differential equation), the most explicit model of the quantum memory is one with two linearly independent quantum states described in terms of the Fermi pseudo-potential at one point. In this model, operations on the quantum memory are accomplished through scattering with both symmetrical and anti-symmetrical incident waves. As a first step toward operating on more than one quantum memory, this model is generalized in two directions. (1) With the Fermi pseudo-potential at one point retained, three linearly independent quantum states are used for the quantum memory. This model of the quantum memory requires three external connections. (2) With a more general potential, operations on the quantum memory with two states are accomplished through scattering with either symmetrical or anti-symmetrical incident waves. This second generalization is important because it is not practical to keep the number of external connections equal to the number of linearly independent quantum states.

Quantum computing (QC) has become an important area of research in computer science because of its potential to provide more efficient algorithmic solutions to certain problems than are possible with classical computing (CC). In particular, QC is able to exploit the special properties of quantum superposition to achieve computational parallelism beyond what can be achieved with parallel CC computers. However, these special properties are not applicable for general computation. Therefore, we propose the use of "hybrid quantum computers" (HQCs) that combine both classical and quantum computing architectures in order to leverage the benefits of both. We demonstrate how an HQC can exploit quantum search to support general database operations more efficiently than is possible with CC. Our solution is based on new quantum results that are of independent significance to the field of quantum computing. More specifically, we demonstrate that the most restrictive implications of the quantum No-Cloning Theorem can be avoided through the use of semiclones.

Progress of optical logic has been anything but uniform or even monotonic. The hope for “all optical computers” was largely abandoned after devastating critiques by Keyes. Over time, optical logic transformed into a very viable niche activity by the needs of optical communication for “all optical” logic and the advent of a critical component: the SOA or Semiconductor Optical Amplifier. I argue that a new phase in this uneven history can be defined - linear (single photon, not multiple entangled photon) quantum optical logic. These can perform conservative, reversible logic operations without energy or time penalties, but cascading requires the irreversible act of measurement, so only single devices or single layers can deliver those advantages.

Exploiting recent advances in quantum trapped-ion technologies, we propose a scalable, fault-tolerant quantum computing architecture that overcomes the fundamental challenges of building a full-scale quantum computer and leaves the fabrication a daunting but primarily an engineering concern. Using a hierarchical array-based design and a quantum teleportation communication protocol, we are able to overcome the primary scalability challenges of reliability, communication, and quantum resource distribution. In particular, we present a reconfigurable quantum circuit substrate, or "quantum FPGA'' (qFPGA) which allows efficient implementation of universal quantum gates and error correction. We use this qFPGA as a basic building block for an array structure that scalably provides communication channels and quantum resource distribution. We exploit a hierarchical combination of ballistic transport of data ions and quantum teleportation to reduce the cost of reliable communication from exponential to polynomial in distance. By using a set of simulation tools we are able to evaluate a hypothetical design of a future general purpose quantum computer and describe the execution of a fault-tolerant Toffoli gate construction. Without considering classical control constraints and assuming best-possible ion-trap parameters our computer consists of level 2 encoded qubits with the Steane \ecc code tightly connected by the teleportation interconnect, and capable of executing a fault-tolerant Toffoli gate in roughly 2.3 seconds. This translates to factoring a 128-bit number in slightly over 40 hours in circuits dominated by Toffoli gates.

The theoretical study of quantum computation has yielded efficient algorithms for traditionally very hard problems. Correspondingly, the experimental work on technologies for implementing quantum computers has yielded many of the essential discrete components. Combining these components to produce an efficient and accurate quantum architecture is an open problem and exploring this design space requires an efficient evaluation framework. To date, all such frameworks have been either highly theoretical (ignoring vital issues like spatial constraints, resource contention, and the durative nature of quantum operations), or limited to systems with less than 40 qubits because of reliance on simulating the exact quantum state of qubits in the system. To address these issues the authors present QUALE, a set of tools for the design and analysis of microarchitectures for ion-trap quantum computers. QUALE allows the user to specify a quantum program in an existing quantum language, apply error correction, schedule the resulting computation on a proposed layout, and determine an upper bound on the expected accuracy of the resulting computation. By conducting analysis on a program-architecture pair QUALE takes into account realistic architectural constraints; by targeting simulation to error as opposed to the whole quantum state, QUALE is able to efficiently simulate large systems containing thousands of quantum bits.

We recently discovered when two ensembles of N qubits are initialized to random phases, then the Cartesian distance metric between the ensemble states is approximately sqrt(2N), with a standard deviation of 1/2. This research relates inner product and quantum ensemble metrics to the “standard distance” metrics defined by correlithm object theory. Correlithm object theory describes how randomly selected points (or COs) in high dimensional bounded spaces can be used as soft tokens to represent states at the ensemble level. The initial CO research was performed using unit N-cubes, but under Air Force SBIR contract, we extended this theory for other bounded metric spaces such as binary N-spaces, complex N-spaces and Hilbert spaces. A quantum encoded CO can be created by initializing an ensemble of qubits based on a phase ensemble of uniformly distributed, randomly chosen phases with values from 0 to 2pi. If a quantum encoded CO token is created as a qubit ensemble Q initialized using a specific phase ensemble P, upon quantum measurement using another phase ensemble of basis states B it produces a binary ensemble A of measurement answers. Multiple trials using the exact same ensembles P and B generate answer ensembles that are correlated with each other, since their distance metric is 70.7% of the binary standard distance of sqrt(N/2). This means that quantum encoded CO tokens survive this measurement process. In contrast, choosing new random ensembles P or B for each trial generates uncorrelated answer ensembles. This paper describes and demonstrates how quantum measurement acts as a noise injection process from the correlithm object perspective.

Current technology for building digital computers is predicted to reach its limit within the next 10 years due to the increasing miniaturization of digital components. By reaching sizes of a few nanometers, electrons stop behaving as particles and start behaving as waves, obeying essentially the principles of Quantum Mechanics, and effects such as interference, superposition and entanglement become dominant. The utilization of those effects allows more that just an evolution of the miniaturization process. It allows for a computational parallelism impossible to be obtained efficiently through classical computational methods or devices. Several algorithms utilizing such effects have been proposed and indicated that Quantum Computation is significantly more efficient at solving certain class of problems than classical computation. Actually, there is not yet any hardware (a quantum computer) able to compute a useful algorithm outside of research labs. A turn-around to that problem is to simulate the behavior of a quantum computer by a classical computer. There are, to this day, a number of quantum computer simulators available which, in general, use the quantum circuit model defined by Deutsch. Just a few of them are universal. We have developed a novel universal quantum circuit simulator, called Zeno, to the design and test of quantum algorithms. Zeno offers a set of features that engulfs most of the features presented by the other existing universal quantum circuit simulators and that also allows it to be used in the design and simulation of quantum channels.

This paper reports the current status of the DARPA Quantum Network, which became fully operational in BBN's laboratory in October 2003, and has been continuously running in 6 nodes operating through telecommunications fiber between Harvard University, Boston University, and BBN since June 2004. The DARPA Quantum Network is the world's first quantum cryptography network, and perhaps also the first QKD systems providing continuous operation across a metropolitan area. Four more nodes are now being added to bring the total to 10 QKD nodes. This network supports a variety of QKD technologies, including phase-modulated lasers through fiber, entanglement through fiber, and freespace QKD. We provide a basic introduction and rational for this network, discuss the February 2005 status of the various QKD hardware suites and software systems in the network, and describe our operational experience with the DARPA Quantum Network to date. We conclude with a discussion of our ongoing work.

For a general entangling probe attacking the BB84 protocol in quantum key distrobution, I show that the simplest quantum circuit representing the optimal entangling probe, and yielding the maximum information gain on the pre-privacy-amplified key, consisting of a single CNOT gate in which the control qubit consists of two polarization-basis states of the signal, the target qubit consists of two probe-photon polarization basis states, and the initial state of the probe is set by the error rate induced by the probe. A method is determined for measuring the appropriate correlated state of the probe. Finally, a possible implementation of the entangling probe is described. the device is a simple special-purpose quantum cryptography.

We describe a robust heralded single photon source based on parametric down conversion of CW 532-nm light in a periodically polled KTP waveguide. Low required pump power (sub-mW), reasonable operational temperature (43oC), high heralding efficiency (60%), and narrow spectral width of the heralded photons (sub-nm) make it an ideal light source for long-distance quantum communications.

Quantum key distribution (QKD) is an emerging technology for secure distribution of keys between users linked by free-space or fiber optic transmission facilities. QKD has usually been designed for and operated over dedicated point-to-point links. However, the commercial world has been developing increasingly sophisticated fiber networks, with basic networking functions such as routing and multiplexing performed in the optical domain. One of the most important practical questions for the future of QKD is to what extent it can benefit from these trends, either to expand the capabilities of dedicated quantum networks, or to avoid the need for dedicated networks by combining quantum and conventional optical signals onto a single infrastructure. In this paper, we report on systematic investigations of these issues using a 1310-nm weak-coherent, phase-encoded B92 prototype QKD system developed by Los Alamos that includes the implementation of error correction, privacy amplification, and authentication. We have demonstrated reconfigurability of QKD networks via optical switching and successful QKD operation in the presence of amplified DWDM signals over 10 km of fiber. We have identified anti-Stokes Raman scattering of the DWDM signals in the fiber as a dominant transmission impairment for QKD, and developed filtering architectures to extend transmission distances to at least 25 km. We have also measured noise backgrounds and polarization variations in network fibers to understand applicability to real-world networks. We will discuss the implications of our results for the choice of QKD wavelengths, wavelength-spacing between QKD and conventional channels, and QKD network architectures.

We describe a free space Quantum cryptography system which is designed to allow continuous unattended key exchanges for periods of several days, and over ranges of a few kilometres. The system uses a four laser faint pulse transmission system running at a pulse rate of 10MHz to generate the required four alternative polarization states. The receiver module similarly automatically selects a measurement basis and performs polarization measurements with four avalanche photodiodes. The controlling software can implement the full key exchange including sifting, error correction, and privacy amplification required to generate a secure key.

In 2003, Bechmann-Pasquinucci introduced the concept of quantum seals, a quantum analogue to wax seals used to close letters and envelopes. Since then, some improvements on the method have been found. We first review the current quantum sealing techniques, then introduce and discuss potential applications of quantum message sealing, and conclude with some discussion of the limitations of quantum seals.

We review our recent work establishing by an explicit many-body calculation for an open quantum-mechanical system of two qubits subject to independent noise modelled by bosonic baths, a newly identified connection between two important quantities in the studies of entanglement and decoherence. We demonstrate that the decay of entanglement is governed by the product of the suppression factors describing decoherence of the subsystems (qubits). This result is a detailed model calculation proving an important and intuitively natural physical property that separated open quantum systems can evolve coherently, quantum mechanically on time scales larger than the times for which they remain entangled. Our result also suggests avenues for future work. Specifically, for multiqubit systems, it is expected that similar arguments should apply "by induction." This will stimulate research to develop appropriate quantitative measures of entanglement, and attempts to quantify entanglement and decoherence in a unified way. We considered one "physically meaningful" measure of two-qubit entanglement, the concurrence. In future research, it would be of interest to obtain similar results for other measures of entanglement as well.

We discuss methodologies for non-demolition measurement of quantum states. Four quantum non-demolition measurement strategies are described namely phase-coupled, polarization-coupled, gain-coupled, and Raman-effect coupled measurement schemes. Qualitative as well as quantitative assessments are presented for each of the measurement schemes in terms of back-action evading, quantum-state preperation, and degration of signal field. Simulation results indicate that quantum non-demolition measurements are realized for low coupling coefficients for each of the four schemes.

A Gaussian statistic, or discriminator, is proposed for conclusively discriminating between two pure quantum states. The discriminator is based on registrations from a limit of an increasing number of weak measurements on a single system. The average error of the discriminator is near that of the optimal conclusive Helstrom discriminator and, in fact, the Gaussian discriminator is the limit point of a class of conclusive discriminators which includes the Helstrom discriminator. The Gaussian discriminator always leaves some post-measurement state (PMS) separation; by contrast, the PMS separation with the Helstrom discriminator is always zero. Simple, closed-form expressions are given for the distribution and error performance of the Gaussian discriminator.

We discuss the relevance of a form of quantum mechanics in finite dimensions based on Weyl's unitary rotations in ray space developed by the author to the construction of unbiased bases for the determination of a quantum state.

The term 'hypermachine' denotes any data processing device (theoretical or that can be implemented) capable of carrying out tasks that cannot be performed by a Turing machine. We present a possible quantum algorithm for a classically non-computable decision problem, Hilbert's tenth problem; more specifically, we present a possible hypercomputation model based on quantum computation. Our algorithm is inspired by the one proposed by Tien D. Kieu, but we have selected the infinite square well instead of the (one-dimensional) simple harmonic oscillator as the underlying physical system. Our model exploits the quantum adiabatic process and the characteristics of the representation of the dynamical Lie algebra su(1,1) associated to the infinite square well.

The quantum Boltzmann equation method is demonstrated by numerically predicting the time-dependent solutions of the velocity and magnetic fields governed by nonintegrable magnetohydrodynamic equations in one spatial dimension. The method allows arbitrary tuning of the value of the viscosity and resistivity transport coefficients without compromising numerical integrity even near the zero dissipation and turbulent regime where shock front discontinuities emerge.

In this paper we develop two topics and show their inter- and cross-relation. The first centers on general notions of the generalized classical signal theory on finite Abelian hypergroups. The second concerns the generalized quantum hyperharmonic analysis of quantum signals (Hermitean operators associated with classical signals). We study classical and quantum generalized convolution hypergroup algebras of classical and quantum signals.