Combining elements of mathematics, computer science, engineering, and physical sciences, quantum information science (QIS) has the potential to provide capabilities far beyond what is possible with the most advanced technologies available today. Quantum science, generally, is the study of the smallest particles of matter and energy; QIS builds on quantum science principles to obtain and process information in ways that cannot be achieved based on classical physics principles. QIS is based on the premise that information science depends on quantum effects in physics. The advantages to using QIS in certain circumstances can be illustrated by the example of quantum computing. Quantum computing is not just "faster" than classical computing. It is not useful for many types of problems where a classical supercomputer would excel. However, there are certain tasks for which the power of quantum computing is unmatched, such as code breaking. This power is derived from quantum computing's use of "qubits" or "quantum bits." Whereas classical computing uses "bits" for data processing, quantum computing uses qubits. The practical difference between a bit and a qubit is that a bit can only exist in one of two states at a time, usually represented by a 1 and a 0, whereas a qubit can exist in both states at one time. This is a phenomenon called "superposition" and it is what allows the power of a quantum computer to grow exponentially with the addition of each bit. Two bits in a classical computer provides four possible combinations—00, 01, 11, and 10, but only one combination at a time. Two bits in a quantum computer provides for the same four possibilities, but, because of superposition, the qubits can represent all four states at the same time, making the quantum computer four times as powerful as the classical computer. So, adding a bit to a classical computer increases its power linearly, but adding a qubit to a quantum computer increases its power exponentially—doubling power with the addition of each qubit. Quantum computing, for all its promise, is still a developing technology (along with other quantum applications). Assembling a working quantum computer is much more difficult than assembling a classical computer. The difficulty is caused by the narrow set of conditions that must exist for a quantum computer to work. For example, the temperature must be exactly 1/100 th of a degree above absolute zero. Also, the slightest vibration can cause a qubit to lose its superposition. Until systems can be developed to maintain the ideal conditions to maintain a qubit, many quantum systems will remain theoretical in nature. Although much of the press coverage of QIS has been devoted to quantum computing, there is more to QIS. Many experts divide QIS technologies into three application areas: Sensing and metrology, Communications, and Computing and simulation. Quantum sensing and metrology include navigation, atomic clocks, gravimeters and gravitational gradiometers, inertial motion units, atomic magnetometers, electron microscopes, technologies to locate subterranean mineral deposits, and quantum-assisted nuclear spin imaging devices. They currently have the largest range of existing and potential commercial products. There are also several products in this category that have been manufactured for decades, making it the most established category. In its report Assessment of the Future Economic Impact of Quantum Information Science , analysts at the Institute for Defense Analysis (IDA) determined that new technologies in quantum metrology and sensing offer improved accuracy compared to products based on classical physics or existing quantum technologies. New QIS technologies are being used for position, navigation, and timing; medical imaging; and research. Some experts believe that the potential markets for these technologies are small because in some cases, traditional technologies remain more attractive due to the higher costs and technical complexity of QIS alternatives. However, others have stated that they believe continued investment and effective coordination between the research community and industry could bring a broad range of QIS-enhanced sensors to the U.S. marketplace by 2021. Quantum key distribution (QKD) is a method of securing communications that uses quantum physics, rather than mathematical algorithms, to safeguard data sent over unprotected networks. However, signals traveling over fiber-optic cable weaken at about 60 miles and must be retransmitted. Quantum repeaters can extend the distance the signal can be sent, but they significantly increase the complexity of the process. The communications are not only secure, but any eavesdropping attempt will destroy the communication, revealing the eavesdropping attempt. The Chinese government has been spending heavily on QKD, but many analysts in North America and Europe do not believe that the benefits over existing nonquantum technologies outweigh the costs associated with QKD, making commercial demand difficult to ascertain. Quantum computing provides an exponentially larger scale than classical computing, which provides advantages for certain applications. Quantum simulation refers to the use of quantum hardware to determine the properties of a quantum system, for example, determining the properties of materials such as high-temperature superconductors, and modeling nuclear and particle physics. However, the current capabilities of quantum computers limit the size of the problems that they can be used to solve. While significant research has been conducted to date by government laboratories, university departments, and large technology companies, as well as small start-ups, it is unlikely that any commercial quantum computing will be widely available before 2025. The government's interest in QIS dates back at least to the mid-1990s, when the National Institute of Standards and Technology (NIST) and the Department of Defense (DOD) held their first workshops on the topic. QIS is first mentioned in the FY2008 budget of what is now the Networking and Information Technology Research and Development Program and has been a component of the program since then. In September 2018, the Department of Energy (DOE) announced that it had committed $218 million to 85 research projects lasting from two to five years. Also in September 2018, the National Science Foundation (NSF) announced that it had awarded $31 million in grants to 33 projects. Eight projects receiving a total of $6 million are engineering projects aimed at creating working quantum information systems (applied research). The remaining $25 million will be distributed to 25 basic research projects. Government QIS basic research is also conducted by NIST, the DOD services, and the Office of the Secretary of Defense. Additionally, the Defense Advanced Research Projects Agency and the Intelligence Advanced Research Projects Activity have funded a series of targeted programs. QIS is a component of the National Strategic Computing Initiative (Presidential Executive Order 13702), which was established in 2015. The White House has issued two reports on QIS strategy, the first under President Obama and the second under President Trump. In July 2016, the National Science and Technology Council (NSTC), under the purview of the White House Office of Science and Technology Policy (OSTP), issued Advancing Quantum Information Science: National Challenges and Opportunities . This report provided a brief description of the QIS disciplines, summarized developments and potential impacts in various fields of technology and areas of basic research, identified impediments to progress and potential approaches to addressing them, surveyed federal investments, and discussed the federal path forward in the context of international and private-sector activity. The report outlined three principles to guide U.S. government QIS R&D: Maintain stable and sustained core programs that can be enhanced as new opportunities appear and restructured as impediments evolve. Sustained core programs will allow established researchers to continue their work, give students confidence that QIS is a field with a future, and provide a solid base for translating laboratory demonstrations into marketable technology. Invest strategically in targeted, time-limited programs to achieve concrete, measureable objectives. Targeted, time-limited programs are an effective mechanism for achieving well-defined technical advances and allow quick adaptation to a changing technological landscape. Closely monitor the field to evaluate the outcome of federal QIS investments and quickly adapt programs to take advantage of technical breakthroughs as they are made. Continued monitoring is required to ensure that the federal strategy for QIS investment remains effective into the future and to avoid technological surprise. The report concluded by stating that QIS should be considered a priority for federal coordination and investment, with particular attention paid to identifying and implementing methods to address impediments to progress and maintaining a commitment to keep the United States at the leading edge of QIS developments. In September 2018, the NSTC issued The National Strategic Overview for Quantum Information Science . The policy opportunities identified in this strategic overview are summarized in Table 1 . According to the report, "following these recommendations, along with detailed planning and coordination made possible by the SCQIS as well as engagement with stakeholders, is crucial for the United States' future success." On November 19, 2018, the Department of Commerce (DOC) Bureau of Industry and Security (BIS or "bureau") released an Advance Notice of Proposed Rulemaking (ANPRM), "Review of Controls for Certain Emerging Technologies." The bureau controls the export of dual-use and other military items through export regulations. This ANPRM seeks public comment on criteria to identify emerging technologies that may be essential to U.S. national security, for example, because they— have potential as conventional weapons or weapons of mass destruction; could provide new methods for intelligence collection; could be used as the basis for new terrorist applications; or could provide the United States with a qualitative military or intelligence advantage. These criteria may be included in possible future export control regulations. The list of categories includes, among many others, a wide range of QIS applications: positioning, navigation, timing, computing, sensing, and encryption. Comments on the ANPRM are due on December 19, 2018. QIS R&D is being pursued at major research centers worldwide, with China and the European Union (EU) having the largest foreign QIS programs. The UK and Canada have also made high-profile investments in QIS R&D, while Australia and the Netherlands have made smaller investments. Even without explicit QIS initiatives, many other countries, including Russia, Germany, and Austria, are making strides in QIS R&D.