Microwave Journal
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Instrument Applications in Quantum for the Aerospace and Defense Industry

September 14, 2020

This article focuses on a couple of key application areas for quantum technology in the aerospace and defense industry. In addition, it covers some of the measurement tools that are used in the development and analysis of performance for quantum-based systems. This article does not cover the physics of the quantum systems but refers to some of the key characteristics of quantum bits (qubits) as they are manipulated and measured (read the previous article in this supplement for the basics on quantum computing).

In general, the application of quantum technology in the aerospace and defense arena aligns well with the current adoption of quantum technologies in computing, sensing and communications. From an aerospace and defense perspective, one of the key application areas for quantum computing includes quantum key distribution (QKD) for encryption of sensitive data and prevention of cyberattacks. The extremely fast speeds of quantum computers for optimization of exponentially challenging algorithms enables them to also be used in the management of military missions and in deep space exploration.

The aerospace industry has for a long time taken advantage of the quantum effects for timing; an example is in the adoption of the cesium atom for precision timing. However, with the advent of the latest advances in the application of quantum mechanical behavior with newer atomic species, these structures offer more secure systems for positioning, navigation and timing.

Overall, quantum technologies are expected to provide several advantages that will include resilient and integrated communication systems and, in addition, open opportunities for precision navigation and timing. Also, providing the aerospace industry with the capability of having advance persistence, long range sensing systems.

CYBERSECURITY AND OPTIMIZED COMPUTATION

Today, cyberattacks can come from a variety of places and in a variety of forms. In Figure 1, two of the typical attackers and sources of cybersecurity threats are shown that include organized crime groups and foreign governments. Due to the potential processing power and sensitivity of quantum technologies, as well as the concept of quantum entanglement, it is expected that quantum computers will allow for the rapid development of highly encrypted communication systems using quantum cryptography. The currently safe and secure classical encryption has the potential of being broken using quantum computing technologies so governments are aggressively pursuing these new solutions.

Figure 1

Figure 1 Quantum key distribution enables encryption and security.

Quantum cryptography is the science of exploiting quantum properties to perform cryptographic tasks. The advantage of quantum cryptography lies in the fact that it allows the completion of various cryptographic tasks that are proven to be impossible using only classical communication. The other area is the application of quantum optimization algorithms that could be used to speed up modeling of aircraft design for the ultimate performance.

Since the development of quantum computing technologies forms the basis for enabling the development of algorithms that offer robust methods of encryption and decryption in the aerospace industry, let’s start with a discussion on these solutions and how they may be applied, as well as how we may provide testing for these platforms. From a quantum mechanics perspective, the properties of “superposition state” and “quantum entanglement” form the basis for enabling the development of encryption and optimized computation algorithms. This implies that the quantum computers that are developed to address these needs would have to ensure that the quality of the qubits are based on providing high fidelity gates with low crosstalk.

In the physical realization of quantum computers, several technologies are used, including superconducting systems, trapped ion systems, spin qubits and neutral atoms. The cryogenic-based systems that operate in the millikelvin temperatures are typically superconducting and spin qubit systems. In some of the aerospace industry applications, trapped ion, superconducting qubits and neutral atom systems are more commonly adopted.

Superconducting qubits can consist of transmon qubits that require complex connection and cryogenic systems to perform operations on the qubit. Ion traps are slightly different and use atomic particles that are confined and suspended in free space using electromagnetic fields and are controlled using complex laser systems.

Figure 2

Figure 2 Simplified block diagram of a quantum computer.

Figure 3

Figure 3 Qubit control and readout hardware.

In order to understand the performance and measurement of these platforms, let’s look at the architecture of a typical quantum computer. From Figure 2, we see the key elements that make up the system include the control hardware for the qubits, the cryogenic chamber that includes the inputs and outputs, and the superconducting quantum computer chip itself. In general, the quantum computer is operated at cryogenic temperatures of ten millikelvin. The quantum computer control and readout are done using microwave pulses provided by control hardware.

The control hardware supplies signals to the system by means of microwave pulses, optical pulses and DC generators usually in the form of unique waveforms. Next, the quantum system requires a readout system that consists of making an excitation coupled with the quantum system. In many quantum error correction experiments, a feedback loop can be created between the control and readout hardware so that adjustments can be made to the control hardware.

Imperfections in the control hardware can affect qubit coherence times: jitter, phase noise, amplitude and temperature stability, noise and frequency accuracy. These problems are compounded as the number of qubits increases and the control system must deal with tens or hundreds of simultaneous control signals applied to these qubits.

To support these requirements, the control hardware that is typically used includes arbitrary waveform generators (AWG) and digitizers. For a quantum computing application, the AWG and digitizers must ensure high gate efficiencies, low latency, phase coherent time-dependent and sequential control pulses. In addition, the measurement and control hardware need to be extensible to allow for the control of several qubits as required in the computation as well as the seamless integration into the QKD distribution code and the cybersecurity algorithms.

This demands that the hardware is modular, allows for the lowest latency, provides excellent phase coherency and customizable software for the control of the quantum computer. In Figure 3, we see an example of the current PXI based AWG and digitizer solutions that has these capabilities.

The PXI AWG and digitizer platform shown in Figure 3 can be programmed at the hardware level using a hardware virtual interface and provides access to the FPGA’s used in the generation of the required waveforms. This addresses the need for low latency from control to readout and ensure ease of synchronization of the waveforms generated.

When utilizing quantum computers for any type of computation, it is important to know the resonance frequencies for each of the qubits that form part of the computer and how long your qubit will remain in a certain state. To characterize the qubit lifetime, Rabi oscillation experiments that help in the tuning of single qubit gates are used.

In Figure 4, we see a measurement of a qubit on an ideal resonance that was measured using a fast-triggered pulse sequence. The experiment involves driving the qubit between two energy states |0> to |1> and |1> to |0> repeatably. The Rabi experiment is such that a series of pulses of different amplitudes are applied to the qubit that is fixed on the resonance frequency.

Figure 4

Figure 4 Qubit resonance and decoherence.

Figure 4 also illustrates the on-resonance pi/2 condition that is determined by selecting an amplitude sweep that is half of what is used for the ideal on-resonance. As an example, the pi/2 pulse resembles the ideal qubit being manipulated from a |0> state into a superposition state |0> + |1>, which is in both the ground and excited state.



Another phenomenon that qubits exhibit is that of decoherence which essentially is the loss of information and can be due to the quantum system environment. One can think of it as the loss of information from the quantum system into the environment and cannot be avoided. However, by understanding the decoherence time, like shown in Figure 4, one can calibrate the qubit to maintain its state while it is being used for the execution of algorithms.

TIMING NAVIGATION AND SENSING

Figure 5

Figure 5 Quantum-based sensing and navigation applications.

When it comes to the navigation and sensing applications, the aerospace industry is turning to the application of quantum physics to provide a more resilient set of solutions that are not easily compromised. There are several quantum-based sensing technologies that are under investigation, and these cover motion, such as acceleration, rotation and gravity, along with electric and magnetic fields and imaging.

A commonly used structure is based on the quantum effect of a magnetic field on a diamond-based nitrogen vacancy structure as shown in Figure 5. It is a highly sensitive structure that enables fast accurate sensing of aircraft, underwater communications and positioning using a gyroscope that senses the Earth’s magnetic field for navigation. It is important to note while navigation and surveying are feasible and being deployed, the magnetic detection of fast-moving objects is not something that has yet to be realized with this technology.

Intercepting communications is still a long way away but presents a real opportunity for the aerospace and defense industry. The fundamental nature of this technology does not allow external interferences and making it a much more secure approach for positioning and navigation.

Another area of adoption for quantum phenomena is the application of the Rydberg atomic effect for sensing electromagnetic energy. This works on the principle of excitation of atoms in a vapor cell to a Rydberg state and can then be used to detect signals that cover anything from 0 to 100 GHz. This concept can be extremely useful in the aerospace and defense industry since it can be used by military personnel to detect any radio communications over this wide frequency range limiting the need to carry additional hardware. One of the challenges facing the full adoption is implementation of compact lasers that are required to excite the atoms into a Rydberg state.

The example in Figure 6 shows a typical application of a diamond-based nitrogen vacancy (NV) structure. That is acousto-optically modulated which excites NV centers sensitive to magnetic fields for spin initialization and readout. A microwave source such as an AWG, is mixed and sends microwave pulses to the diamond providing coherent spin manipulation. Next, the collection lens receives the emitted light pulses which are sent to a photodetector to be converted into an electric signal. The electrical signals are returned to the digitizer and sent to a computer for data interpretation.

Figure 6

Figure 6 Nitrogen vacancy control and readout.

RADAR AND SATELLITE COMMUNICATION

The application of quantum technologies in the satellite communication space is in its early stages of research. The concepts of quantum entanglement and QKD are proving to be very attractive advantages for quantum-based communication systems. These two concepts can provide highly encrypted communication channel between ground stations and satellites in space.

Another path for quantum communications is quantum illumination that is the archetype for quantum communication as we know it today and works in line with quantum networks. A free space quantum network would enable the ability to communicate with satellites over very long distances.

Figure 7

Figure 7 Aircraft detection using quantum illumination.

Figure 8

Figure 8 Real-time scope with display of Rabi oscillation waveforms.

In the case of radar applications as shown in Figure 7, quantum illumination may be used and is subject to similar aspects of transmission as with classical radar. The path to detect unknown objects through air requires a method known as two-mode squeezing. A high frequency pump emits a photon that is split through spontaneous parametric down-conversion to two lower frequency beams called the signal and the idler. Entanglement of two photon pairs dramatically increases sensitivity. The idler is immediately measured and kept at a base station, while the signal is sent as a probe toward the unknown object. The signals both pass through a receiver and an entanglement detector, which are measured by a digitizer.

ADDITIONAL DEVELOPMENT TOOLS

In the discussion thus far, the focus has been on a couple key areas for adoption of quantum technology in the aerospace and defense industries. Next, some of the complimentary hardware that enables the development of quantum-based solutions is covered. In the development of the quantum computer for instance, it was noted that AWGs and digitizers play a key role in control of the qubit states.

A real-time oscilloscope is key in establishing the waveforms for the Rabi oscillation experiments for example. In Figure 8, the application of a real-time oscilloscope that shows the different pulses to help establish the qubit resonance is shown. The result is a consistent Rabi measurement as the schedule of pi pulses increases. This marks a consistency in the resonance frequency that is tuned to the qubit that can now oscillate around the Bloch sphere proportional to the amplitude of the pulse.

Resonator measurements are key to ensuring the highest quality materials designs for the Josephson junctions used in the deployment of quantum systems. Therefore, vector network analyzers (VNA) play a key role since these measurements do not require time-domain operation. One of the challenges that is under research is the ability to make a calibrated measurement at the very low cryogenic temperature.

Figure 9

Figure 9 Benchtop and modular VNA used for quantum resonator measurements.

Figure 10

Figure 10 Equipment used to qualify quantum system designs.

Figure 9 shows the application of the VNA in the development of superconductor microwave resonators. These resonators form the core for understanding the material loss properties when developing qubits and are also used for qubit readout. Finally, in Figure 10 other complimentary hardware is used to ensure we have the highest quality materials and models as well as the appropriate noise levels are shown. Several instruments may be used, these include semiconductor analyzer, DC power analyzers and bit error rate testers.

SUMMARY

For the aerospace and defense industry, the adoption of quantum computers for development of safe and secure communication will be a fertile area of research, while the fast speeds offered by quantum computers for optimization of exponentially challenging algorithms is leading the way. In the area of sensing navigation and positioning, there are clear opportunities and materials that allow for the development of newer, less vulnerable positioning and navigations solution.

In the satellite and radar space, this is clearly in the early stages of adoption for some of the quantum technologies, although there are single photon systems that are more evolved in this space. Finally, in the development of quantum solutions, there is a growing need for more software tools, like Labber, that allow for the ease of control of hardware, while providing a suitable platform for the development of the different quantum control experiments.

Suren Singh received his BSEE from University of Durban-Westville, Durban South Africa in 1985. He completed a Graduate Diploma at the University of Witwatersrand, Johannesburg South Africa in December 1992. He then went on to complete his MSEE at the University of Witwatersrand, Johannesburg in 1995. Suren has been with the Hewlett-Packard Company, Agilent Technologies and now Keysight Technologies since 1986. His experience includes application engineering, product design, manufacturing and test process development for microwave hybrid microcircuits. He also held the position of an application specialist and system architect, focused on the terahertz measurement solutions for Keysight. In addition, he is responsible for the metrology products for performance network analyzers, including both calibration and verification and both ambient and cryogenic temperatures. More recently, Suren has been appointed as the business and application development lead for the Keysight quantum initiative focused on the aerospace industry. He has been working closely with the Quantum Engineering Solutions team within Keysight to bring solutions to the quantum research and development that is part of the aerospace industry.