Our Research
Goals of the Center
Among the four pillars of quantum technology—quantum computing, communication, sensing, and simulation—quantum communication offers the clearest path toward integration with current information technology. In our envisioned intermediate quantum hybrid systems, the advantages of elementary forms of quantum communication can be combined with state-of-the-art networking techniques to form quantum-enhanced information distribution networks. This task, however, requires a cross-disciplinary approach in order to identify the key engineering problems in which using quantum protocols can boost the performance of existing communication systems. Multiple Stony Brook faculty members and their teams are spearheading research efforts and combining their expertise and core research activities in three major areas: (I) computer engineering and networking, (II) quantum communication, and (III) scaling of quantum devices to create the quantum technology of the future.
Computer Science and Networking
Current Members:
Dr. Vladimir Korepin(SUNY Stony Brook – Department of Physics and Astronomy), Dr. Aruna Balasubramanian, Dr. Michael Ferdman, Dr. Himanshu Gupta, Dr. Omkant Pandey, Dr. C.R. Ramakrishnan (SUNY Stony Brook – Department of Computer Science), and Dr. Tzu-Chieh Wei (SUNY Stony Brook – Department of Physics and Astronomy).
Research: This team will identify key problems at the juncture of QIS and current networking systems. We have already identified important synergic applications and research questions:
Quantum networks for classical communication
When links that can reliably transmit quantum information are realized, we can use them as building blocks for higher-bandwidth classical communication. Existing techniques such as dense coding describe a way to increase channel capacity (up to a factor of two) over classical links. Recent advances have increased this capacity via the use of multiple-qubit systems. Analogous to dense coding, we can devise methods to transmit large volumes of classical data via quantum links of limited capacity, such that the receiver may extract an arbitrarily chosen (but fixed number of) bits of information from that data. We will design novel communication protocols, including generalizations of teleportation or dense coding, to facilitate cost-effective communication of more qubits/bits across arbitrary nodes in such a network.
Quantum networks for secured communication/computation
Quantum links permit tamper-evident and statistically-secure information transmission. We will study secure communication in the context of end-to-end, secure, tamper-proof, or tamper-evident classical/quantum channels to achieve the security properties while minimizing costs. This work will explore the design of new cryptographic schemes (e.g., multi-party computation protocols with information-theoretic security) over hybrid networks consisting of quantum-secured and classical channels and investigate whether we can leverage such networks for post-quantum security in standard cryptographic schemes.
Quantum networks for distributed systems
Consensus protocols are widely used for data replication in distributed systems, from federated data centers to cloud infrastructure. Distributed leader election consensus permits data replication with consistency, load balancing, recoverability, and resiliency that are otherwise not achievable in systems spanning large geographic areas. These protocols rely on the participants’ ability to reach a common state by exchanging information over an unreliable network and agreeing on an object’s value. Quantum links offer a basis for a new breed of consensus protocols, with entangled quantum states replacing multiple rounds of classical information exchange needed to achieve consensus, and we will expand on prior related work on this topic.
Photonic network interconnect for quantum processors
We envision quantum photonic networks to provide a fast interconnect between individual quantum processors in order to create large, scalable, distributed, and parallel quantum computers. With such a network interconnect, it will be possible to configure and use a virtual quantum computer with k qubits such that the qubits are drawn from a set of physical quantum computers connected by a quantum network. Research areas include determining the kind of quantum computing power that results from such a network, examining whether we can quantify the computational limits of such a network, and investigating how the issues of coherence and errors are handled/resolved by such a network.
QUANTUM ALGORITHMS
Quantum search: Low Depth Quantum Search
Grover's quantum search algorithm provides a quadratic speedup over classical algorithm. The computational complexity is based on the number of queries to the oracle. However, depth is a more practical metric for quantum computer. Based on Grover's algorithm, we propose several new quantum search algorithms which have lower depth. The algorithm can be divided into several steps. Each step consists of a new initialization of the input, which potentially decreases the error for limited coherent time quantum computer. Under some condition, the algorithm within measurements still reaches lower depth compared with Grover's algorithm. We also consider several methods to parallel running the quantum search algorithm. For details see https://arxiv.org/pdf/1908.04171.pdf.
Quantum systems out of equilibrium
Quench velocity in spin chains & Spin chains essential for high energy physics
XXX spin chain with spin s=-1 appears as an effective theory of Quantum Chromodynamics. It is equivalent to lattice nonlinear Schroediger's equation: interacting chain of harmonic oscillators [bosonic]. In thermodynamic limit each energy level is a scattering state of several elementary excitations [lipatons]. Lipaton is a fermion: it can be represented as a topological excitation [soliton] of original [bosonic] degrees of freedom, described by the group Z2. We also provide the CFT description (including local quenches) and Yang-Yang thermodynamics of the model. For details see https://arxiv.org/pdf/1909.00800.pdf.
Entanglement in spin chains
We introduce a new model of interacting spin 1/2. It describes interaction of three nearest neighbors. The Hamiltonian can be expressed in terms of Fredkin gates. The Fredkin gate (also known as the CSWAP gate) is a computational circuit suitable for reversible computing. Our construction generalizes Ramis Movassagh's work. Our model can be solved by means of Catalan combinatorics in the form of random walks on upper half of a square lattice [Dyck walks]. Each Dyck path can be mapped on a wave function of spins. The ground state is an equally weighted superposition of Dyck walks [instead of Motzkin walks]. We can also express it as a matrix product state. We further construct the model of interacting spins 3/2 and greater half-integer spins. The models with higher spins require coloring of Dyck walks. We construct SU(k) symmetric model [here k is the number of colors]. The leading term of the entanglement entropy is then proportional to the square root of the length of the lattice [like in Shor-Movassagh model]. The gap closes as a high power of the length of the lattice. For details see https://arxiv.org/pdf/1605.03842.pdf.
Quantum Entanglement Generation and Distribution in Large Quantum Networks
Current Members:
Dr. Eden Figueroa and Dr. Dominik Schneble (SUNY Stony Brook – Department of Physics and Astronomy), Dr. Dimitrios Katramato, Dr. Andrei Nomerotski and Dr. Paul Stankus (Brookhaven National Laboratory).
Research: Our Center will have access to the largest quantum light-matter interfaces network in the United States, providing an excellent test bed for the construction of quantum cryptographic systems and quantum entanglement distribution protocols. We aim to finalize a quantum repeater network of quantum light-matter interfaces at Brookhaven National Lab and Stony Brook University. The network will be interconnected using fiber quantum links and will demonstrate the full potential of quantum repeaters for relaying quantum information. This quantum repeater network will be based upon ultracold and scalable room-temperature quantum memories, bridged to work with entangled photons at telecom wavelengths. The test bed of our ideas will be a large-scale quantum network connecting several locations in Stony Brook University and Brookhaven National Laboratory. By using atomic quantum memories to enhance the swapping of the polarization entanglement of pairs of flying photons, our implementation will take a major leap in quantum communication by distributing entanglement over long distances without detrimental losses. The recent technological developments needed to achieve high-fidelity quantum operation at room temperature are a unique strength of our collaboration.
Developing quantum networking hardware infrastructure
We are utilizing existing optical fiber infrastructure and have already deployed entanglement sources and quantum memories in several buildings on the BNL campus, quantum connecting the Physics and Instrumentation buildings with the Scientific Data and Computation Center (SDCC). A similar local quantum network has been developed in parallel on the Stony Brook campus that connects Physics, Communications Engineering (ECC), the Basic Science tower, and the Center of Excellence of Wireless and Information Technology (CEWIT). With the quantum communication channels in place, we will use photonic entanglement sources to simultaneously store and retrieve quantum correlations in four quantum memories on both campuses. The existing infrastructure will be the test bed to develop the applications and research questions mentioned in the previous subsection.
Scaling of Quantum Communication Devices
Current members:
Dr. Xuedong Hu (SUNY Buffalo – Department of Physics), Dr. Vasili Perebeinos (SUNY Buffalo – Department of Electrical Engineering), Dr. Quanxi Jia (SUNY Buffalo – Department of Materials Design and Implementation), and Dr. Spyros (Spyridon) Galis (SUNY Poly – Department of Nanoengineering).
Research: The creation of large quantum networks interconnecting scalable quantum devices is one of the main objectives of our envisioned center. A major barrier to overcome is the ability to create entanglement at the scales required for entanglement distribution over hundreds of kilometers. Of existing technologies, quantum materials-based quantum devices are ideal for creating large quantum networks. Connecting such scalable technology to large well-controlled atomic systems exhibiting long coherence times is a viable pathway toward the construction of scalable, large quantum systems.
Solid-state single-photon emitters
We will explore quantum dot systems, 2D materials, and high-spectral-purity emitters from engineered defects/ions in nanostructured wide-bandgap materials. The underlying theme is incorporating deterministic positioning and nanoplasmonic engineering at a fundamental level to modify the local electromagnetic environment for Purcell enhancement, significantly enhancing single-photon emission rate and angular distribution. The proposed tailorable nanophotonic structures provide high design adaptability, tunability, and integration capabilities with silicon nanophotonics. Additionally, we propose using engineered single defects in 2D materials to achieve electrically pumped single-photon emission sources and integrating them into quantum communication circuits. The tunability of the emitted light wavelength can be achieved by external gates via the Stark effect and by applying strain, targeting tunable, electrically controlled, single-photon light sources for quantum communications. Furthermore, existing quantum coherent devices are mostly based on semiconducting and superconducting nanocircuits and work in the microwave frequency range. To integrate these known quantum coherent devices with an optical frequency quantum network, we envision the need for quantum coherent transducers with high fidelity. Optomechanical oscillators have been proposed for such transducers. The proposed center will explore whether 2D materials could be used to build mechanical transducers when properly tailored. Specifically, both electronic and mechanical properties will be explored to establish their coupling with external fields.
Scaling of light-matter interfaces
We will demonstrate hybrid quantum interconnects, where photons generated in the 2D materials will be interfaced with atomic experiments, forming elementary quantum networks. These devices will be applied in the expansion of quantum networks of many such quantum devices in which entanglement is shared among multiple network nodes. Our long-term vision is to implement a larger network of light-matter quantum interfaces expanding on the existing quantum nodes at Stony Brook University and BNL.