About

Professor Rajveer Nehra leads the Quantum Information Systems Lab at the University of Massachusetts Amherst. His research focuses on the experimental and theoretical development of quantum information science and technology (QIST), with an emphasis on the scalable implementation of quantum technologies at room temperature. His work involves utilizing quantum optics, quantum information science, and nanophotonic engineering tools to develop quantum information systems for applications in computation, communication, sensing, and metrology. As the head of an interdisciplinary team of physicists, engineers, and computer scientists, Prof. Nehra contributes to advancing fundamental science and creating new technologies that offer significant advantages across various fields.

Research topics

• Materials science
• Optics
• Computer Science
• Physics
• Optoelectronics
• Telecommunications

Selected publications

• Ultra-broadband, Low-loss Wavelength Combiners and Filters: Novel Designs and Experiments in Thin-film Lithium Niobate

  arXiv (Cornell University) · 2026-03-27

  preprintOpen accessSenior author

  Thin-film lithium niobate (TFLN) has emerged as a leading platform for large-scale programmable photonic circuits for quantum and classical applications. As circuits scale in complexity, low-loss routing of broadband pump and signal fields becomes essential. Here, we present closed-form analytical models and experimentally demonstrate compact, fast-quasi-adiabatic driving-optimized wavelength combiners and filters operating at the fundamental harmonic (FH, 1550 nm) and second-harmonic (SH, 775 nm) wavelengths. Our designs achieve ultra-low loss below 0.06 dB across a 90 nm bandwidth at FH, while maintaining extinction ratios exceeding 25 dB. At SH, the loss remains below 0.12 dB over a 45 nm bandwidth with extinction ratios greater than 19 dB. Devices fabricated on a 300-nm TFLN platform exhibit added loss below 0.1 dB across 1550 - 1600 nm, with minimum values of 0.04 dB around 1580 nm and 0.021 dB at 775 nm. Combined with recent advances in on-chip quantum state generation, low-loss interferometers, and detection, these results enable high-fidelity quantum photonic circuits on the TFLN platform.

  PublisherDOI

• Ultra-broadband, Low-loss Wavelength Combiners and Filters: Novel Designs and Experiments in Thin-film Lithium Niobate

  arXiv (Cornell University) · 2026-03-27

  articleOpen accessSenior author

  Thin-film lithium niobate (TFLN) has emerged as a leading platform for large-scale programmable photonic circuits for quantum and classical applications. As circuits scale in complexity, low-loss routing of broadband pump and signal fields becomes essential. Here, we present closed-form analytical models and experimentally demonstrate compact, fast-quasi-adiabatic driving-optimized wavelength combiners and filters operating at the fundamental harmonic (FH, 1550 nm) and second-harmonic (SH, 775 nm) wavelengths. Our designs achieve ultra-low loss below 0.06 dB across a 90 nm bandwidth at FH, while maintaining extinction ratios exceeding 25 dB. At SH, the loss remains below 0.12 dB over a 45 nm bandwidth with extinction ratios greater than 19 dB. Devices fabricated on a 300-nm TFLN platform exhibit added loss below 0.1 dB across 1550 - 1600 nm, with minimum values of 0.04 dB around 1580 nm and 0.021 dB at 775 nm. Combined with recent advances in on-chip quantum state generation, low-loss interferometers, and detection, these results enable high-fidelity quantum photonic circuits on the TFLN platform.

  PublisherOA PDF

• Rethinking Quantum Networking with Advances in Fiber Technology

  arXiv (Cornell University) · 2026-03-24

  articleOpen access

  Recent comparisons of quantum repeater protocols have highlighted the strong near-term potential of multiplexed two-way architectures for long-distance quantum communication. At the same time, advances in hollow-core fiber (HCF) technology motivate a re-examination of the physical transmission medium as an architectural lever in quantum network design. In this work, we compare emerging anti-resonant HCFs against conventional silica single-mode fibers (SMFs) in multiplexed two-way quantum repeater networks. We evaluate their performance under both telecom and memory-native transmission, accounting for frequency-conversion overheads, coupling efficiencies, memory decoherence, and operational noise. We find that HCF significantly outperforms SMF across a wide range of regimes. With memory-native transmission, HCF yields up to an order of magnitude improvement in secret-key rate per channel use under realistic conversion efficiencies. Even at telecom wavelengths, HCF enables larger optimal repeater spacing, improving rate--cost tradeoffs and reducing repeater requirements. We further quantify the role of memory quality, hardware efficiency, detector and conversion losses, and two-qubit gate noise in shaping these gains. These results show that recent advances in HCF materially expand the design space of practical terrestrial quantum repeater networks.

  PublisherOA PDF

• Rethinking Quantum Networking with Advances in Fiber Technology

  arXiv (Cornell University) · 2026-03-24

  preprintOpen access

  Recent comparisons of quantum repeater protocols have highlighted the strong near-term potential of multiplexed two-way architectures for long-distance quantum communication. At the same time, advances in hollow-core fiber (HCF) technology motivate a re-examination of the physical transmission medium as an architectural lever in quantum network design. In this work, we compare emerging anti-resonant HCFs against conventional silica single-mode fibers (SMFs) in multiplexed two-way quantum repeater networks. We evaluate their performance under both telecom and memory-native transmission, accounting for frequency-conversion overheads, coupling efficiencies, memory decoherence, and operational noise. We find that HCF significantly outperforms SMF across a wide range of regimes. With memory-native transmission, HCF yields up to an order of magnitude improvement in secret-key rate per channel use under realistic conversion efficiencies. Even at telecom wavelengths, HCF enables larger optimal repeater spacing, improving rate--cost tradeoffs and reducing repeater requirements. We further quantify the role of memory quality, hardware efficiency, detector and conversion losses, and two-qubit gate noise in shaping these gains. These results show that recent advances in HCF materially expand the design space of practical terrestrial quantum repeater networks.

  PublisherDOI

• Data for Four-Photon Subtraction from Picosecond Squeezed Vacuum Demonstrating Wigner Negativity without Loss Correction

  Zenodo (CERN European Organization for Nuclear Research) · 2026-04-12

  datasetOpen access

  Data for generating figures in the paper. plot_wigners.ipynb - code for generating the figures from the datarho_0tap_bootstrap_1000.npy - density matrices without postselectionrho_0photon_bootstrap_1000.npy - density matrices for subtracting 0 photonsrho_1photon_bootstrap_1000.npy - density matrices for subtracting 1 photonrho_2photon_bootstrap_1000.npy - density matrices for subtracting 2 photonsrho_3photon_bootstrap_1000.npy - density matrices for subtracting 3 photonsrho_4photon_bootstrap_1000.npy - density matrices for subtracting 4 photonswigners_mean.npy - calculated average Wigner functions for evaluating negativitywigners_std.npy - calculated standard deviation for the average Wigner functions for evaluating negativity

  PublisherDOI

• Data for Four-Photon Subtraction from Picosecond Squeezed Vacuum Demonstrating Wigner Negativity without Loss Correction

  Zenodo (CERN European Organization for Nuclear Research) · 2026-04-12

  datasetOpen access

  Data for generating figures in the paper. plot_wigners.ipynb - code for generating the figures from the datarho_0tap_bootstrap_1000.npy - density matrices without postselectionrho_0photon_bootstrap_1000.npy - density matrices for subtracting 0 photonsrho_1photon_bootstrap_1000.npy - density matrices for subtracting 1 photonrho_2photon_bootstrap_1000.npy - density matrices for subtracting 2 photonsrho_3photon_bootstrap_1000.npy - density matrices for subtracting 3 photonsrho_4photon_bootstrap_1000.npy - density matrices for subtracting 4 photonswigners_mean.npy - calculated average Wigner functions for evaluating negativitywigners_std.npy - calculated standard deviation for the average Wigner functions for evaluating negativity

  PublisherDOI

• All-optical Loss-tolerant Distributed Quantum Sensing

  npj Quantum Information · 2026-01-22

  articleOpen access1st authorCorresponding

  Distributed quantum sensing (DQS) leverages quantum resources to estimate an unknown global property of a networked quantum sensor beyond the classical limit. We propose and analyze an all-optical resource-efficient scheme for the next-generation DQS systems. Our method utilizes phase-sensitive optical parametric amplifiers (OPAs) and linear interferometers and achieves the sensitivity close to the optimal limit, as determined by the quantum Fisher information of the entangled resource state. Furthermore, it utilizes high-gain OPA-assisted detection, offering critical advantages of increased bandwidth and loss tolerance, in contrast to conventional methods employing balanced homodyne detection (BHD). We show the efficacy of our proposal for displacement sensing and show its loss tolerance against high levels of photon loss, thus circumventing the major obstacle in current BHD-based approaches. Our architectural analysis shows that our scheme can be realized with current quantum photonic technology.

  PublisherOA PDFDOI

• All-optical measurement-device-free feedforward enabling ultra-fast quantum information processing

  Optics Express · 2025-01-28 · 9 citations

  articleOpen access

  Utilizing feedforward to perform adaptive quantum operations on one entangled state according to the measurement result of the other state enables measurement-based quantum information processing (QIP). Until now, the bandwidth of feedforward in optical QIP has been limited to around 100 MHz by measurement with electronics. A potential alternative is the utilization of an optical parametric amplifier (OPA). This optical device eliminates the need for electronic measuring devices and enables all-optical broadband feedforward. In this paper, we demonstrate a variable squeezing gate with an operation bandwidth of 1.3 THz by all-optical measurement-device-free feedforward. We utilize a periodically poled lithium niobate waveguide as a broadband OPA and perform continuous phase locking in our optical system. Experimental results demonstrate that our all-optical QIP operates at a THz clock frequency, representing a major step toward the realization of an ultra-fast quantum computer.

  PublisherDOI

• Octave dual-wavelength multimode interferometers for nonlinear integrated photonics

  2025-09-16 · 1 citations

  article

  A compact dual-wavelength multimode interference (MMI) coupler based on a thin-film lithium niobate (TFLN) platform is proposed for efficient operation at both 1550 nm and its second harmonic, 775 nm. The device functions as a wavelength multiplexer and demultiplexer, which addresses the growing need for broadband and low-loss wavelength separation in nonlinear and quantum photonic circuits. Conventional wavelength division multiplexing (WDM) structures often suffer from high insertion loss and limited fabrication tolerance, particularly when handling widely separated wavelengths. Here, we present an MMI that serves as a multiplexer/demultiplexer that enables high-performance wavelength management within a single device. The structure achieves ultra-low insertion losses below 0.5 dB, high contrast exceeding 15 dB, and a broad 3-dB bandwidth of 15 nm at both wavelengths. According to the strong nonlinear and electro-optic properties of TFLN, this dual-wavelength MMI provides a low-loss alternative to traditional WDM approaches for integrated nonlinear and quantum photonic circuits.

  PublisherDOI

• Scalable Optical Quantum State Synthesizer with Dual-Mode Resonator Memory

  Open MIND · 2025-01-01 · 1 citations

  articleOpen access

  Optical quantum computing is a promising approach for achieving large-scale quantum computation. While Gaussian operations have been successfully scaled, the inherently weak nonlinearity in opticsmakes generating highly non-Gaussian states a critical challenge for universality and fault tolerance. Here, we propose and experimentally demonstrate a scalable method to generate optical non-Gaussian states with a resonator-based quantum memory that supports continuous-time storage and retrieval, in contrast to conventional loop-based memories. We introduce a dual-mode operation of the memory, enabling both storage and entangling functionalities within a single device. By employing a time-domain-multiplexed approach, we successfully demonstrate both cat and Gottesman-Kitaev-Preskill breeding protocols in a scalable fashion, marking a key step toward quantum error correction. Our experiment also marks the first full demonstration of an optical resonator memory performing writing, storage, and readout operations.We validate the memory by storing squeezed single-photon states with up to 93% total efficiency, and measure an energy relaxation time T₁ = 2.3 μs and dephasing time T_φ = 0.96 μs. These results establish a scalable pathway to generating complex non-Gaussian states required for fault-tolerant optical quantum computing. Beyond computation, our techniques provide new tools for enhancing quantum communication, sensing, and metrology.

  PublisherDOI

Frequent coauthors

• Olivier Pfister

  University of Virginia

  58 shared

• Miller Eaton

  University of Virginia

  52 shared

• Alireza Marandi

  45 shared

• Luis Ledezma

  34 shared

• Ryoto Sekine

  22 shared

• Aye Win

  University of Oklahoma

  19 shared

• Qiushi Guo

  California Institute of Technology

  16 shared

• Niranjan Sridhar

  15 shared

Labs

• Quantum Information Systems LabPI