Abstract

As secure space communications becomes more desirable, quantum based communications systems have the potential to become a high performing option. NASA/GSFC with its partner institutions is pursuing a variety of technology thrusts to enable the practical application of quantum communications in future NASA missions. This paper will discuss some of those technology areas. We will discuss methods being developed by GSFC and University of Kansas for securing and auto-synchronizing communication over free-space optics using quantum key distribution and chaotic systems. In such a scenario, the security of the system would stem from the sensitivity to initial conditions. Furthermore, specific windows of single chaotic runs can be harvested to be used with encoder/decoder in a cyclic manner. Not only would the security of such a system be unique, the initial conditions can be transmitted via a quantum key distribution to add another layer of security to the system. We will discuss work being performed by GSFC and Michigan State University in analysis and development of solid-state quantum communications materials and devices. These will be necessary for devices capable of processing and routing quantum information on-board a spacecraft or within a quantum-capable ground station. In recent years, advancements in the understanding of quantum properties has led to a wide range of promising applications. One such application is orbital angular momentum (OAM) for secure optical communications being researched by partners at University of Wyoming and University of Illinois-Chicago The utilization of OAM properties can be done via highly precise function values that can then be modulated using different constellations. Opportunities for quantum communications demonstrations exists in a variety of possible venues from balloons to CubeSats. We will discuss the potential for a low cost, high altitude balloon-to-balloon quantum communications demonstration to be carried out under the University of Wyoming Space Grant.

Acronyms/Abbreviations

Avalanche

1. Introduction

There has been an explosion of research in the area of quantum computing and quantum communications. There is the groundbreaking work by Paul Kwiat, et. al. in the Quantum Information Group at the University of Illinois, some of which as sponsored by NASA with collaborators at JPL [1] , [2] , [3] . There is also the highly significant research, broad-based research in the characteristics of quantum space links conducted in Austria at the Institute for Quantum Optics and Quantum Information [4] . Within NASA, GSFC and its partners are also engaged in research involving quantum phenomena including quantum sensors, quantum computing, and quantum communications. In this paper, we describe some of the activities related to quantum communications that are under investigation within the Exploration and Space Communications (ESC) division of GSFC. We are a group of part-time researchers developing technology for future US laboratory experiments in quantum communications and computing while training students in these technologies. We include university partners and GSFC civil servant and contractors.

The main purpose of this paper is to acquaint a broad audience of some of the activities under way at GSFC and capabilities that are available to advance quantum communications technologies.

We have a deep background in nanomaterials, simulation and modelling of quantum materials, information theory, quantum mechanics, and novel forms of communications. All of our activities include student involvement through the use of strategic student internships. Each of the external collaborator institutions supplies undergraduate and graduate students to work alongside professionals at GSFC. The students get involved in mission planning and design, systems engineering, and technology development. The students are directly supervised by former interns who have become NASA employees. The former interns develop their project management and technology development skills. Current interns can see a path to future NASA employment, and we maintain a pipeline of excellent students that will replenish the NASA workforce as it ages. Given a generic block diagram for a quantum communications architecture as shown in Fig.1 , all of the activities being undertaken fit somewhere in one or more blocks of the architecture. Fig. 1 . Generic architecture for a quantum communications system. It applies to both space and ground applications

The professionals on the GSFC team have been involved in a variety of classical optical communications projects including the Lunar Laser Communications Demonstration [5] in 2013 and the upcoming Laser Communications Relay Demonstration [6] to be launched in 2020. We leverage that experience in the development of quantum communications for space.

1.1 Goals

The main goals of this research program are:  Provide an educational experience for US undergraduate and graduate students in quantum theory and phenomena through real-life projects to develop quantum entangled communications systems for flight  Develop a low-cost approach to the development of quantum entangled communications systems that can evolve into fully functional quantum entangled communications systems for NASA  Develop a self-supporting network of collaborators pursuing various aspects of quantum communications  Support the US National Quantum Initiative

2. Synergy With The Classical Optical Communications Projects

The development of a quantum optical communications at GSFC requires taking a path that leverages the classical optical communications work. This path can leverage on developments in classical laser communications. Advances in classical coding theory using LDPC could continue to be implemented in a quantum communications scheme as well as classical optical communication modulation techniques such as mary Pulse Position Modulation (PPM), Differential Quadrature Phase Shift Keying (DQPSK) and others. Our plan is to leverage technology from the LCRD mission into quantum entanglement deployment efforts.

3. Student Intern Project -Quantum Entangled Stratospheric Telecommunications (Quest)

A team of students from the collaborator institutions came to GSFC in the summer 2019 to begin development of a student project to implement quantum-entangled communications. The activity involves a partnership with the University of Wyoming High Altitude Balloon research conducted under their National Science Foundation Grant. The goal is a balloon-to-balloon demonstration. Students were assigned to develop all parts of the mission. The important point that was stressed by NASA was the large amount of work required to develop a workable mission around the quantum entanglement experiment. Thus, the graduate physics major was assigned to the science team and the engineering majors were tasked to work interactively with the science team to achieve the mission objectives. This is how NASA projects typically work: Engineers come up with solutions to achieve science objectives.

It was also decided that the student team would work from a defined set of requirements. This would focus the team on developing an implementation approach around requirements.

3.1 Mission Requirements And Student Implementation Path

The intern team was given a set of Level 1 requirements as guidance in developing the project. The Level 1 requirements were decomposed into Level 2 requirements by the Systems Engineer. The Level 1 requirements are shown in Table 1 . At least one of the two points must include a payload on a flying balloon as part of the demonstration. 3

The team shall determine the distance between source and destination as part of their design. 4 Quantum entanglement has to be demonstrated at 600-770 nm wavelength 5 Implement a quantum security protocol as part of the demonstration. 6

The team shall develop a block diagram of the demonstration with all the pieces and their links and interconnections with a description, and a description of the concept of operations for the mission. 7

The communications payload has to be retrievable and reusable.

8

As a minimum, the payload must include a quantum entangled modulator and transmitter for the transmit function and a quantum entangled demodulator and receiver for the receive function. The functions can be separate enclosures if necessary. 9

There shall be a data source that produces classical data to feed the transmit function and a method to determine bit error rate of the demonstration 10 The PI and the team shall document the criteria for proving that successful entanglement has occurred over the link between source and destination. 11 There shall be an atmospheric monitoring system for the visible to Near IR wavelengths that can provide cloud free line of sight data to the mission 12 Develop an integrated schedule and a rough order of magnitude cost estimate for the entire mission.

The interns decided upon a two-balloon mission concept as shown in Fig. 2 . The mission concept is still undergoing analysis against potential alternatives e.g. ground-to-balloon quantum entanglement. The implementation trades over the space of payload mass, buoyancy, altitude, mission lifetime and payload recovery without damage were performed by the University of Wyoming students. Fig. 2 . The student high-level concept for a two-balloon experiment that would involve one way communications from a transmitter balloon to a receiver balloon with fully autonomous operations at an experiment altitude from 15km to 20km with no ground communications. Experiment results to be retrieved upon retrieval of the payloads.

3.2 Summary Of Quantum Entanglement Experiment

The University of Wyoming developed the concept for quantum entanglement experiment as summarized in Fig. 3 . The underlying protocol is being simulated and refined as part of his dissertation work.

3.3 Point Ahead And Track

The importance and difficulties of having two balloons rising independently find and acquire each other was stressed to the team. New Mexico State led the development of the point ahead and track (PAT) concept shown in Fig. 4 . It is based on known spacecraft PAT approaches for optical communications Additional analysis and work will be required to refine the concept.

3.4 Balloon Payload Design

The PAT system will only work if the payload is capable of correcting the pointing of the transmit and receive optics in azimuth and elevation. Adding systems to control the pointing of the balloons during ascent would severely impact the mass and power budget. The concept for the mechanical design is shown in Fig. 5 . Fig. 5 . High Altitude Balloon Payload design. The mechanical structure will allow for azimuth/elevation pointing compensations.

3.4 Electronics And Detector Development

The project requires single photon detectors however, the budget severely limits the available options. The decision to go with visible wavelength lasers was tied to the availability of silicon avalanche photodiodes (APD) that could be operated in Geiger mode. Unfortunately, the parts for completing this development were not received until the end of the summer internship. Team members from New Mexico State, Michigan State and University of Illinois -Chicago performed:  DC characterization of silicon APDs at low temperature (solid CO2 temperatures) and developed design concepts for two single photon APD quenching circuits from the published literature  Developed a Spice model for a quenched APD  Applied machine learning algorithms to perform device selection on capacitors, inductors and transistors to optimize the APD quenching circuit designs. Fig. 6 summarizes the QUEST team preliminary design. The payload mass was estimated at 22.5 kg and power requirements at 72W. This estimate provides some room for mass and power growth. The transmitter and receiver balloons have a quantum communications channel at optical and a RF channel for PAT, position info and quantum channel check bit information.

3.6 Future Work For The Quest Project.

Graduating students that are leaving the team will be replaced and work towards a Preliminary Design Review (PDR)-level of design is ongoing. GSFC is continuing to build up the lab capabilities with a goal of being able to perform quantum entangled communications in 400-800 nm and 1550 nm wavelengths. Planning for a CubeSat version of QUEST is expected to start within one year.

4. Securing And Auto-Synchronizing Communication Over Free-Space Optics Using Quantum Key Distribution And Chaotic Systems

University of Kansas team has been working with NASA/GSFC on developing chaotic communications over free space optical links and implementing quantum key distribution as a key security factor. The potential for chaotic communications has broad extensibility into the quantum communications field.

Chaotic communication was first presented by E. N. Lorenz in 1963. It displays well defined, but extremely complex dynamic behaviours. It can be likened to broadband noise-like signals similar to spread-spectrum signals [7] . It has multi-path fading resistance, unpredictability, and extreme sensitivity to initial conditions. Thus, it is difficult for unintentional receivers to synchronize to the chaotic signal. However, parameter synchronization is essential for both TX and RX, hence QKD is applied to perform that synchronization. A detailed description of chaotic communications is beyond the scope of this paper and the reader is referred to references [8] , [9] , [10] , [11] . Fig. 7 depicts a future heterogeneous constellation with a variety of classical, chaotic and quantum-optical communications.

The significance of this work is the use of QKD to eliminate the security weakness around transmitting the chaotic synchronization parameters over classical channels. The University of Kansas has already done extensive research on chaotic communications including FPGA implementations of the protocol. To harden a BB84 implementation using only two bases between Alice and Bob, NASA/GSFC source coding into a preshared Huffman codeword dictionary and encryption using the Rivest, Shamir, Adelman (RSA) algorithm to strengthen the encryption with pre-shared keys.

The proposed system architecture is shown in Fig. 8 . Data shown are from Matlab simulations using this architecture.

4.1 Qkd Model For Chaotic Parameter Exchange

The methodology of chaotic communication protocol is described in detail in [12] . Of particular interest in this paper is the QKD implementation which is responsible for exchanging the set of synchronization parameters, ℤ where ℤ = { , , , (0), (0), (0)} (1) and , ,

EQUATION (3): Not extracted; please refer to original document.

EQUATION (4): Not extracted; please refer to original document.

The parameter exchange protocol is shown in Fig.10 as originally described in [12] . Fig. 9 . Use of pre-shared secret codebook for encrypting/decrypting the synchronization data. The position of the codewords is assumed to have been randomized by Alice and de-randomized by Bob. Fig. 10 . Quantum Key Distribution models for chaotic parameter exchange

In step 1, Alice encodes the synchronization parameters into classical binary format, translates to qubits, and then transmits them to Bob using the agreed upon basis. Bob has the basis with no knowledge of the order of qubit coding. Bob randomly measures the qubits and transmits the results back to Alice. In step 2, Alice receives and compares Bob’s results, encrypts the matches (M) to form the quantum encryption key (Key), In step 3, Alice sends the Key to Bob. In step 4, Alice encrypts the synchronization parameters using the Key and the pre-shared Huffman dictionary codewords (H) described in (4), translates, and transmits the associated qubits to Bob. Bob then decodes the qubits using his preshared Huffman dictionary and the Key. Fig. 11 demonstrates the sensitivity of chaotic communications to the initial conditions. These simulations included the QKD synchronization parameter exchange.

4.3

Future work for free space optical chaotic communications with QKD.

The current plan is to perform bench top testing using the University of Kansas FPGA implementation of chaotic communications and the GSFC quantum communication lab facilities. This will be followed by a quantum entangled QKD over free space optical chaotic communications.

Additional work will also be conducted in simulating a noisy quantum channel in parallel with the classical AWGN channel.

A summer intern project by interns from University of Wyoming and University of Illinois-Chicago has bred a research thrust to investigate paths to implementing a scheme using a cyclic chaotic encoder/decoder over photonic orbital angular momentum (OAM). OAM is a quantum property of light. The goal is chaotic encoding and QKD for security and OAM for multi-gigabit per second optical data transmission [13] .

5. Flying Qubit Heterostructures And Evaluation Of Candidate Quantum Nanomaterials For Solid-State Quantum Entangled Communications

A flying qubit in general refers to qubits in motion as opposed to a stationary qubit. The Michigan State team is partnering with GSFC to lead research in quantum nanomaterials. The current state of the research is in the pre-laboratory experiment, analytical phase. [14] . These investigations are concentrated on potential implementations into quantum modems and communications over short distances. The goal is to combine quantum 1D channels fabricated in III-V heterostructures over Surface Acoustic Wave layers (SAW). Such devices will find applications in development of quantum communications ground stations, for example.

The flying qubit approach utilizes a (SAW) for the capture and transport of a single or few electron(s) from a reduced dimensionality electron pool. This concept was derived from experimentally demonstrated single electron capture and transport by SAW waves, over distances in the micron range [15] . Fig. 12 shows the geometry of one finite width channel structure under analysis. Fig.12 . Model for evaluating a 2D quantum well consisting of GaAsAlGaAs layers in the z-direction and split-gate to provide additional confinement in the ydirection.

SAW-driven qubits is one of the areas of emphasis in this research. We are developing techniques that will allow fabrication of test structures that combine quantum transport materials of interest over conventional SAW devices as shown in Fig. 13 . Fig. 13 . The use of a (SAW Device) piezoelectric resonator coupled to the metallocene films for quantum transport with the potential to overcome coherence length limitations through orbital coupling between the metallocene units.

5.1 Future Work In The Quantum Nanomaterials Area.

GSFC and Michigan State are researching candidate materials to support a range of entanglement and hyperentanglement phenomena, e.g. metallocenes with spin and excited Raman emission. Working with the GSFC Cryogenics Branch these investigations will be extended into the low K ( < 6 K) temperature regions.

The team is investigating bulk properties of materials that could indicate favourable quantum entanglement performance [16] , [17] . This includes doping candidate materials into sol-gel matrices using processes developed the GSFC authors [18] , [19] Ongoing simulations of candidate materials and material system for propagating quantum states and implementation of quantum entanglement is being pursued at the molecular level with density functional theory, simulation of potential energy surfaces, and a other analyses using the Amsterdam Modelling Suite from Software for Chemistry and Materials [20] . Perkin-Elmer ChemOffice is being used for 2D and 3D modelling MM2, MM94 energy minimization and other analyses. The goal is to develop consistent go/no go criteria for selection of candidate materials for laboratory evaluation, whenever possible, although some molecules, e.g., transition metal cyclopentadienyls are difficult to simulate accurately at the molecular level.

Simulation activities generally start with analysis of the ground state and excited state orbital configurations, HOMO and LUMO occupation and band gap (if any). Then depending upon the phenomena under analysis, e.g. tautomerism, then additional analyses on the transition state will be performed. An example of one of the steps in the process is shown Fig. 14 . It is part of a 1D potential energy scan which will be used to examine the tautomeric transition of azobenzene as a possible quantum entanglement mechanism.

6. Conclusions

NASA/GSFC and its partner institutions are undertaking a broad range of research activities in the areas of investigating quantum phenomena for quantum communications. We look forward to hearing from potential collaborators and stakeholders for ideas, advice, and funding to advance research in their areas of interest.

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Page 8 of 10 Potential Energy Surface (PES) scan for trans-azobenzene. This is one step in determining the cis-to transtransition characteristics as part of the evaluation for suitability for quantum transport.

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th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019. Copyright ©2019 by the International Astronautical Federation (IAF). All rights reserved.

th International Astronautical Congress (IAC), Washington D.C., United States, 21-25 October 2019. Copyright ©2019 by the International Astronautical Federation (IAF). All rights reserved.