Faculty Directory

The Photonic Quantum Systems group investigates applications of quantum information theory to quantum optics, to design systems that strive to attain the fundamental precision limits of photonic information processing, governed by quantum mechanics. We are interested in the mathematical foundations of quantum information and estimation theories, evaluating fundamental performance limits governed by the laws of physics by treating information-bearing light as a quantum mechanical object, and in designing, evaluating and building proof-of-concept systems in our laboratory that aim to approach such quantum-limited performance, with applications ranging quantum-enhaced classical optical communications, quantum networking, photonic sensing using squeezed light, and quantum-limited resolution in passive imaging. Our research often involves innovations cross-cutting multiple disciplines such as information theory, quantum optics, physics of atomic systems, error correction theory, and network theory.

My research interests are in pursuing fundemental performance limits when light is used to extract, carry and process information. Some examples of topics are as follows:

1. Quantum information and estimation theory: foundations of Bayesian quantum estimation, quantum enhanced change-point detection, entanglement in noisy graph states, distributed manipulations of stabilizer states for sensing, and more.
2. Designing error correction codes and quantum-enhanced joint-detection receivers for classical optical communications.
3. Quantum communications and associated research questions surrounding quantum repeaters, quantum network architectures, interfaces between photonic qubits and quantum memories, and quantum error correction codes for entanglement distillation.
4. Use of non-classical light sources, such as squeezed light and entanglement derived from squeezing, in photonic sensing systems such as radars, LiDARs, fiber-optic gyroscopes, scanning-probe microscopes and more.
5. Systems and methods to approach quantum-limited resolution of passive imaging systems with applications in astronomy, microscopy, and spectral imaging, using pre-detection adaptive multi-mode linear transformations of the information-bearing light.
6. Topics surrounding photonic quantum computing: preparation of fault-tolerant cluster states leveraging percolation theory, error correcting codes for all-photonic repeaters, photonic graph state preparation using quantum emitters.

Here are some of the current sponsored projects in our group.

I will be teaching a new course at UMD for the Spring 2025 semester, called Information in a Photon. This course will be open to both graduate (ENEE 739G) and undergraduate students (ENEE 439G), and will be ideal for ECE students who would like to get a feel for why quantum treatment of light in the contexts of information processing (digital communications, sensing, imaging, etc.) offers fundamentally more powerful insights, and the design of systems with better performance than what is possible otherwise. No prior background in quantum mechanics, optics or information theory is necessary, but students who have a strong background in probability and linear algebra will find it the easiest to navigate the material.

Selected Publications:

1. Quantum enhanced classical communications:

• S. Guha, “Structured optical receivers to attain superadditive capacity and the Holevo limit,” Physical Review Letters 106, 240502 (2011).
• A. Cox, Q. Zhuang, C. Gagatsos, B. A. Bash, and S. Guha, “Transceiver designs to attain the entangle- ment assisted communications capacity”, Phys. Rev. Applied 19, 064015 (2023).
• M. Wilde and S. Guha, “Polar codes for classical quantum channels,” IEEE Transactions on Information Theory, vol. 59, no. 2, 1175–1187 February (2013).
• M. Wilde, P. Hayden and S. Guha, “Information trade-offs for optical quantum communication,” Physical Review Letters 108, 140501 (2012).

• J. Chen, J. L. Habif, Z. Dutton, R. Lazarus and S. Guha, “Optical codeword demodulation with error rates below standard quantum limit using a conditional nulling receiver,” Nature Photonics 6, 374– 379 (2012).

2. Quantum communications and networking:

• S. Guha, H. Krovi, Z. Dutton, C. A. Fuchs, J. A. Slater, C. Simon and W. Tittel, “Rate-loss analysis of an ecient quantum repeater architecture,” Physical Review A 92, 022357 (2015).
• M. Takeoka, S. Guha and M. M. Wilde, “Fundamental rate-loss tradeoffs for optical quantum key distri- bution,” Nature Communications 5, 5235 (2014).
• P. Dhara, D. R. Englund and S. Guha, "Entangling quantum memories via heralded photonic Bell measurement", Phys. Rev. Research 5, 033149 (2023)
• S. Guha, P. Hayden, H. Krovi, S. Lloyd, C. Lupo, J. H. Shapiro, M. Takeoka and M. M. Wilde, “Quantum enigma machines and the locking capacity of a quantum channel,” Physical Review X 4, 011016 (2014).
• M. Pant, H. Krovi, D. Englund, and S. Guha, “Rate-distance tradeoffs and resource costs for all-optical quantum repeaters,” Physical Review A, 95, 102304 (2017).
• B. A. Bash, A. H. Gheorghe, M. Patel, J. L. Habif, D. Goeckel, D. Towsley and S. Guha, “Quantum- secure covert communication on bosonic channels,” Nature Communications 6, 8626 (2015).

3. Percolation theory and its applications:

• M. Pant, D. Towsley, D. Englund, S. Guha, “Percolation thresholds for photonic quantum computing,” Nature Communications 10 (1), 1070 (2019).
• S. Guha, D. Towsley, C. Capar, A. Swami and P. Basu, “Spanning connectivity in a multilayer network and its relationship to site-bond percolation,” Physical Review E 93, 062310 (2016).
• S. Guha, P. Basu, C.-K. Chau and R. Gibbens, “Green Wave Sleep Scheduling: Optimizing Latency and Throughput in Duty Cycling Wireless Networks,” IEEE Journal of Special Areas in Communica- tions (JSAC), Vol. 29, No. 8, September (2011).
• A. Patil, M. Pant, D. R. Englund, D. Towsley, and S. Guha, “Entanglement generation in a quantum network at distance-independent rate,” Nature npj Quantum Information volume 8, Article number: 51 (2022).

• A. Mohseni-Kabir, M. Pant, D. Towsley, S. Guha, A. Swami, “Percolation Thresholds for Robust Net- work Connectivity”, Journal of Statistical Mechanics: Theory and Experiment, 013212 (2021).

4. Quantum limits of imaging:

• W. He, C. N. Gagatsos, D. Wilson, and S. Guha, "Optimum classical beam-position sensing", Phys. Rev. Applied 22, L041004 (2024).
• M. R. Grace, and S. Guha, “Quantum-Optimal Object Discrimination in Sub-Diffraction Incoherent Imaging,” Physical Review Letters, Phys. Rev. Lett. 129, 180502 (2022).
• K. K. Lee, C. N. Gagatsos, S. Guha, and A. Ashok, “Quantum-inspired Multi-Parameter Adaptive Bayesian Estimation for Sensing and Imaging,” IEEE Journal of Selected Topics in Signal Processing (2022).
• A. Sajjad, M. R. Grace, and S. Guha, "Quantum limits of parameter estimation in long-baseline imaging", Phys. Rev. Research 6, 013212 (2024)
• A. Sajjad, M. R Grace, Q. Zhuang, S. Guha, "Attaining quantum limited precision of localizing an object in passive imaging", Phys. Rev. A 104, 022410 (2021)

5. Quantum enhanced photonic sensing:

• S. Guha and B. I. Erkmen, “Gaussian-state quantum-illumination receivers for target detection,” Physical Review A 80, 052310 (2009).
• Z. Dutton, J. H. Shapiro and S. Guha, “LADAR resolution improvement using receivers enhanced with squeezed-vacuum injection and phase-sensitive amplification,” Journal of Optical Society of America (JOSA) B, special issue on Quantum Optical Information Technologies, Vol. 27, No. 6, (2010).
• M. R. Grace, C. N. Gagatsos, Q. Zhuang, S. Guha, “Quantum-Enhanced Fiber-Optic Gyroscopes Using Quadrature Squeezing and Continuous Variable Entanglement,” Phys. Rev. Applied 14, 034065 (2020).
• M. R. Grace, C. N. Gagatsos, and S. Guha, "Entanglement-enhanced estimation of a parameter embedded in multiple phases", Phys. Rev. Research 3, 033114 (2021).
• S. Hao, H. Shi, C. N. Gagatsos, M. Mishra, B. A. Bash, I. Djordjevic, S. Guha, Q. Zhuang, Z. Zhang, “Demonstration of Entanglement-Enhanced Covert Sensing,” Phys. Rev. Lett 129, 010501 (2022).