@article{21747,
  abstract     = {Entanglement does not always require one particle per party. It was predicted some 30 years ago that a single photon traversing a beam splitter could violate a Bell inequality. Although initially debated, single-photon nonlocality was eventually demonstrated via homodyne measurements. Here, we present an alternate realization that avoids the complexity of homodyne measurements and potential loopholes in their implementation. We violate a Bell inequality by performing joint measurements on two copies of the same single-photon entangled state, where one photon acts as a phase reference for the other, making it self-referential. We observe CHSH parameters of 2.71 = 0.09 and 2.23 = 0.07, depending on the joint measurements implemented. This offers a perspective on single-photon nonlocality and a more accessible experimental route, potentially applicable to general mode-entangled states in diverse platforms.},
  author       = {Kun, Daniel and Strömberg, Karl T and Dakić, Borivoje and Walther, Philip and Rozema, Lee A.},
  issn         = {2334-2536},
  journal      = {Optica},
  number       = {4},
  pages        = {745--751},
  publisher    = {Optica Publishing Group},
  title        = {{Testing single-photon entanglement using self-referential measurements}},
  doi          = {10.1364/OPTICA.586172},
  volume       = {13},
  year         = {2026},
}

@article{20840,
  abstract     = {Probing the possibility of entanglement generation through gravity offers a path to tackle the question of whether gravitational fields possess a quantum mechanical nature. A potential realization necessitates systems with low-frequency dynamics at an optimal mass scale, for which the microgram-to-milligram range is a strong contender. Here, after refining a figure-of-merit for the problem, we present a 1-milligram torsional pendulum operating at 18 Hz. We demonstrate laser cooling its motion from room temperature to 240 microkelvins, surpassing by over 20-fold the coldest motions attained for oscillators ranging from micrograms to kilograms. We quantify and contrast the utility of the current approach with other platforms. The achieved performance and large improvement potential highlight milligram-scale torsional pendulums as a powerful platform for precision measurements relevant to future studies at the quantum-gravity interface.},
  author       = {Agafonova, Sofya and Rosello, Pere and Mekonnen, Manuel and Hosten, Onur},
  issn         = {2399-3650},
  journal      = {Communications Physics},
  publisher    = {Springer Nature},
  title        = {{One-milligram torsional pendulum toward experiments at the quantum-gravity interface}},
  doi          = {10.1038/s42005-026-02514-w},
  volume       = {9},
  year         = {2026},
}

@article{20797,
  abstract     = {Quantum key distribution (QKD) offers a theoretically secure method to share secret keys, yet practical implementations face challenges due to noise and loss over long-distance channels. Traditional QKD protocols require extensive noise compensation, hindering their industrial scalability and lowering the achievable key rates. Alternative protocols encode logical qubits in noise-resilient states but at the cost of using many physical qubits, increasing susceptibility to loss and limiting transmission distance. In this work, we introduce a logical-qubit encoding that uses antisymmetric Bell states in the continuous photonic degrees of freedom, frequency and time. By leveraging the continuous space, we overcome this noise-loss robustness trade-off by minimizing the number of photons per logical qubit while optimizing the encoding resilience over noise fluctuations. We analyze the security of our encoding and demonstrate its robustness compared to existing state-of-the-art protocols. This approach provides a path toward scalable, efficient QKD implementations under realistic noise conditions.},
  author       = {Seabrook, Hannah and Lavie, Emilien and Strömberg, Karl T and Stafford, Matthew P. and Rubino, Giulia},
  issn         = {2331-7019},
  journal      = {Physical Review Applied},
  number       = {2},
  publisher    = {American Physical Society},
  title        = {{Surpassing the loss-noise robustness trade-off in quantum key distribution}},
  doi          = {10.1103/xq2l-r4r7},
  volume       = {24},
  year         = {2025},
}

@article{19636,
  abstract     = {This summary of the second Terrestrial Very-Long-Baseline Atom Interferometry (TVLBAI) Workshop provides a comprehensive overview of our meeting held in London in April 2024 (Second Terrestrial Very-Long-Baseline Atom Interferometry Workshop, Imperial College, April 2024), building on the initial discussions during the inaugural workshop held at CERN in March 2023 (First Terrestrial Very-Long-Baseline Atom Interferometry Workshop, CERN, March 2023). Like the summary of the first workshop (Abend et al. in AVS Quantum Sci. 6:024701, 2024), this document records a critical milestone for the international atom interferometry community. It documents our concerted efforts to evaluate progress, address emerging challenges, and refine strategic directions for future large-scale atom interferometry projects. Our commitment to collaboration is manifested by the integration of diverse expertise and the coordination of international resources, all aimed at advancing the frontiers of atom interferometry physics and technology, as set out in a Memorandum of Understanding signed by over 50 institutions (Memorandum of Understanding for the Terrestrial Very Long Baseline Atom Interferometer Study).},
  author       = {Abdalla, Adam and Abe, Mahiro and Abend, Sven and Abidi, Mouine and Aidelsburger, Monika and Alibabaei, Ashkan and Allard, Baptiste and Antoniadis, John and Arduini, Gianluigi and Augst, Nadja and Balamatsias, Philippos and Balaž, Antun and Banks, Hannah and Barcklay, Rachel L. and Barone, Michele and Barsanti, Michele and Bason, Mark G. and Bassi, Angelo and Bayle, Jean Baptiste and Baynham, Charles F.A. and Beaufils, Quentin and Beldjoudi, Sélyan and Belić, Aleksandar and Bennetts, Shayne and Bernabeu, Jose and Bertoldi, Andrea and Bigard, Clara and Bigelow, N. P. and Bingham, Robert and Blas, Diego and Bobrick, Alexey and Boehringer, Samuel and Bogojević, Aleksandar and Bongs, Kai and Bortoletto, Daniela and Bouyer, Philippe and Brand, Christian and Buchmueller, Oliver and Buica, Gabriela and Calatroni, Sergio and Calmels, Léo and Canizares, Priscilla and Canuel, Benjamin and Caramete, Ana and Caramete, Laurentiu Ioan and Carlesso, Matteo and Carlton, John and Carman, Samuel P. and Carroll, Andrew and Casariego, Mateo and Chairetis, Minoas and Charmandaris, Vassilis and Chauhan, Upasna and Chen, Jiajun and Chiofalo, Maria Luisa Maria Luisa Marilù and Ciampini, Donatella and Cimbri, Alessia and Cladé, Pierre and Coleman, Jonathon and Constantin, Florin Lucian and Contaldi, Carlo R. and Corgier, Robin and Dash, Bineet and Davies, G. J. and De Rham, Claudia and De Roeck, Albert and Derr, Daniel and Dey, Soumyodeep and Di Pumpo, Fabio and Djordjevic, Goran S. and Döbrich, Babette and Dornan, Peter and Doser, Michael and Drougakis, Giannis and Dunningham, Jacob and Duspayev, Alisher and Easo, Sajan and Eby, Joshua and Efremov, Maxim and Elertas, Gedminas and Ellis, John and Entin, Nicholas and Fairhurst, Stephen and Fanì, Mattia and Fassi, Farida and Fayet, Pierre and Felea, Daniel and Feng, Jie and Flack, Robert and Foot, Chris and Freegarde, Tim and Fuchs, Elina and Gaaloul, Naceur and Gao, Dongfeng and Gardner, Susan and Garraway, Barry M. and Garrido Alzar, Carlos L. and Gauguet, Alexandre and Giese, Enno and Gill, Patrick and Giudice, Gian F. and Glasbrenner, Eric P. and Glick, Jonah and Graham, Peter W. and Granados, Eduardo and Griffin, Paul F. and Gué, Jordan and Guellati-Khelifa, Saïda and Gupta, Subhadeep and Gupta, Vishu and Hackermueller, Lucia and Haehnelt, Martin and Hakulinen, Timo and Hammerer, Klemens and Hanımeli, Ekim T. and Harte, Tiffany and Hartmann, Sabrina and Hawkins, Leonie and Hees, Aurelien and Herbst, Alexander and Hird, Thomas M. and Hobson, Richard and Hogan, Jason and Holst, Bodil and Holynski, Michael and Hosten, Onur and Hsu, Chung Chuan and Huang, Wayne Cheng Wei and Hughes, Kenneth M. and Hussain, Kamran and Hütsi, Gert and Iovino, Antonio and Isfan, Maria Catalina and Janson, Gregor and Jeglič, Peter and Jetzer, Philippe and Jiang, Yijun and Juzeliūnas, Gediminas and Kaenders, Wilhelm and Kalliokoski, Matti and Kehagias, Alex and Kilian, Eva and Klempt, Carsten and Knight, Peter and Koley, Soumen and Konrad, Bernd and Kovachy, Tim and Krutzik, Markus and Kumar, Mukesh and Kumar, Pradeep and Labiad, Hamza and Lan, Shau Yu and Landragin, Arnaud and Landsberg, Greg and Langlois, Mehdi and Lanigan, Bryony and Leone, Bruno and Le Poncin-Lafitte, Christophe and Lellouch, Samuel and Lewicki, Marek and Lien, Yu Hung and Lombriser, Lucas and Asamar, Elias Lopez and Lopez-Gonzalez, J. Luis and Lu, Chen and Luciano, Giuseppe Gaetano and Lundblad, Nathan and De J. López Monjaraz, Cristian and Lowe, Adam and Mackoit-Sinkevičienė, Mažena and Maggiore, Michele and Majumdar, Anirban and Makris, Konstantinos and Maleknejad, Azadeh and Marchant, Anna L. and Mariotti, Agnese and Markou, Christos and Matthews, Barnaby and Mazumdar, Anupam and Mccabe, Christopher and Meister, Matthias and Mentasti, Giorgio and Menu, Jonathan and Messineo, Giuseppe and Meyer-Hoppe, Bernd and Micalizio, Salvatore and Migliaccio, Federica and Millington, Peter and Milosevic, Milan and Mishra, Abhay and Mitchell, Jeremiah and Morley, Gavin W. and Mouelle, Noam and Müller, Jürgen and Newbold, David and Ni, Wei Tou and Niehof, Christian and Noller, Johannes and Odžak, Senad and Oi, Daniel K.L. and Oikonomou, Andreas and Omar, Yasser and Overstreet, Chris and Puthiya Veettil, Vishnupriya and Pahl, Julia and Paling, Sean and Pan, Zhongyin and Pappas, George and Pareek, Vinay and Pasatembou, Elizabeth and Paternostro, Mauro and Pathak, Vishal K. and Pelucchi, Emanuele and Pereira Dos Santos, Franck and Peters, Achim and Pichery, Annie and Pikovski, Igor and Pilaftsis, Apostolos and Pislan, Florentina Crenguta and Plunkett, Robert and Poggiani, Rosa and Prevedelli, Marco and Rafelski, Johann and Raidal, Juhan and Raidal, Martti and Rasel, Ernst Maria and Renaux-Petel, Sébastien and Richaud, Andrea and Rivero-Antunez, Pedro and Rodzinka, Tangui and Roura, Albert and Rudolph, Jan and Sabulsky, Dylan and Safronova, Marianna S. and Sakellariadou, Mairi and Salvi, Leonardo and Sameed, Muhammed and Sarkar, Sumit and Schach, Patrik and Schäffer, Stefan Alaric and Schelfhout, Jesse and Schilling, Manuel and Schkolnik, Vladimir and Schleich, Wolfgang P. and Schlippert, Dennis and Schneider, Ulrich and Schreck, Florian and Schwartzman, Ariel and Schwersenz, Nico and Sergijenko, Olga and Sfar, Haifa Rejeb and Shao, Lijing and Shipsey, Ian and Shu, Jing and Singh, Yeshpal and Sopuerta, Carlos F. and Sorba, Marianna and Sorrentino, Fiodor and Spallicci, Alessandro D.A.M. and Stefanescu, Petruta and Stergioulas, Nikolaos and Stoerk, Daniel and Thaivalappil Sunilkumar, Hrudya and Ströhle, Jannik and Tam, Zoie and Tandon, Dhruv and Tang, Yijun and Tell, Dorothee and Tempere, Jacques and Temples, Dylan J. and Thampy, Rohit P. and Tietje, Ingmari C. and Tino, Guglielmo M. and Tinsley, Jonathan N. and Tintareanu Mircea, Ovidiu and Tkalčec, Kimberly and Tolley, Andrew J. and Tornatore, Vincenza and Torres-Orjuela, Alejandro and Treutlein, Philipp and Trombettoni, Andrea and Ufrecht, Christian and Urrutia, Juan and Valenzuela, Tristan and Valerio, Linda R. and Van Der Grinten, Maurits and Vaskonen, Ville and Vázquez-Aceves, Verónica and Veermäe, Hardi and Vetrano, Flavio and Vitanov, Nikolay V. and Von Klitzing, Wolf and Wald, Sebastian and Walker, Thomas and Walser, Reinhold and Wang, Jin and Wang, Yan and Weidner, C. A. and Wenzlawski, André and Werner, Michael and Wörner, Lisa and Yahia, Mohamed E. and Yazgan, Efe and Zambrini Cruzeiro, Emmanuel and Zarei, M. and Zhan, Mingsheng and Zhang, Shengnan and Zhou, Lin and Zupanič, Erik},
  issn         = {2196-0763},
  journal      = {EPJ Quantum Technology},
  publisher    = {Springer Nature},
  title        = {{Terrestrial Very-Long-Baseline Atom Interferometry: Summary of the second workshop}},
  doi          = {10.1140/epjqt/s40507-025-00344-3},
  volume       = {12},
  year         = {2025},
}

@article{19733,
  abstract     = {One of the most striking quantum phenomena is superposition, where one particle simultaneously inhabits different states. Most methods to verify coherent superposition are indirect, in that they require the distinct states to be recombined. Here, we adapt an xor game, in which a “test” photon is placed in a superposition of two orthogonal spatial modes, and each mode is sent to separated parties who perform local measurements on their modes without reinterfering the original modes. We show that by using a second identical “measurement” photon the parties are nonetheless able to verify if the test photon was placed in coherent superposition of the two spatial modes. We then turn this game into a resource-efficient verification scheme, obtaining a confidence that the particle is superposed which approaches unity exponentially fast. We demonstrate our scheme using a single photon, obtaining a 99% confidence that the particle is superposed with only 37 copies. Our work shows the utility of xor games to verify quantum resources, allowing us to efficiently detect quantum superposition without reinterfering the superposed modes.},
  author       = {Kun, Daniel and Strömberg, Karl T and Spagnolo, Michele and Dakić, Borivoje and Rozema, Lee A. and Walther, Philip},
  issn         = {2469-9934},
  journal      = {Physical Review A},
  number       = {5},
  publisher    = {American Physical Society},
  title        = {{Direct and efficient detection of quantum superposition}},
  doi          = {10.1103/PhysRevA.111.L050402},
  volume       = {111},
  year         = {2025},
}

@misc{20842,
  abstract     = {Probing the possibility of entanglement generation through gravity offers a path to tackle the question of whether gravitational fields possess a quantum mechanical nature. A potential realization necessitates systems with low-frequency dynamics at an optimal mass scale, for which the microgram-to-milligram range is a strong contender. Here, after refining a figure-of-merit for the problem, we present a 1-milligram torsional pendulum operating at 18 Hz. We demonstrate laser cooling its motion from room temperature to 240~microkelvins, surpassing by over 20-fold the coldest motions attained for oscillators ranging from micrograms to kilograms. We quantify and contrast the utility of the current approach with other platforms. The achieved performance and large improvement potential highlight milligram-scale torsional pendulums as a powerful platform for precision measurements relevant to future studies at the quantum-gravity interface.},
  author       = {Agafonova, Sofya},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Research Data for: 'One-milligram torsional pendulum toward experiments at the quantum-gravity interface'}},
  doi          = {10.15479/AT-ISTA-20842},
  year         = {2025},
}

@phdthesis{20798,
  author       = {Wald, Sebastian},
  isbn         = {978-3-99078-075-6},
  issn         = {2663-337X},
  keywords     = {entanglement-enhanced atom interferometry, cavity QED, spin-squeezing, dipole trap, quantum optics},
  pages        = {152},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Atoms in a propagating-wave cavity for squeezed Mach-Zehnder atom interferometry}},
  doi          = {10.15479/AT-ISTA-20798},
  year         = {2025},
}

@article{14802,
  abstract     = {Frequency-stable lasers form the back bone of precision measurements in science and technology. Such lasers typically attain their stability through frequency locking to reference cavities. State-of-the-art locking performances to date had been achieved using frequency modulation based methods, complemented with active drift cancellation systems. We demonstrate an all passive, modulation-free laser-cavity locking technique (squash locking) that utilizes changes in spatial beam ellipticity for error signal generation, and a coherent polarization post-selection for noise resilience. By comparing two identically built proof-of-principle systems, we show a frequency locking instability of 5×10<jats:sup>−7</jats:sup> relative to the cavity linewidth at 10 s averaging. The results surpass the demonstrated performances of methods engineered over the last five decades, potentially enabling an advancement in the precision control of lasers, while creating avenues for bridging the performance gaps between industrial grade lasers with scientific ones due to the afforded simplicity and scalability.},
  author       = {Diorico, Fritz R and Zhutov, Artem and Hosten, Onur},
  issn         = {2334-2536},
  journal      = {Optica},
  keywords     = {Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials},
  number       = {1},
  pages        = {26--31},
  publisher    = {Optica Publishing Group},
  title        = {{Laser-cavity locking utilizing beam ellipticity: accessing the 10<sup>−7</sup> instability scale relative to cavity linewidth}},
  doi          = {10.1364/optica.507451},
  volume       = {11},
  year         = {2024},
}

@article{14980,
  abstract     = {Precision sensing and manipulation of milligram-scale mechanical oscillators has attracted growing interest in the fields of table-top explorations of gravity and tests of quantum mechanics at macroscopic scales. Torsional oscillators present an opportunity in this regard due to their remarked isolation from environmental noise. For torsional motion, an effective employment of optical cavities to enhance optomechanical interactions—as already established for linear oscillators—so far faced certain challenges. Here, we propose a concept for sensing and manipulating torsional motion, where exclusively the torsional rotations of a pendulum are mapped onto the path length of a single two-mirror optical cavity. The concept inherently alleviates many limitations of previous approaches. A proof-of-principle experiment is conducted with a rigidly controlled pendulum to explore the sensing aspects of the concept and to identify practical limitations in a potential state-of-the art setup. Based on this study, we anticipate development of precision torque sensors utilizing torsional pendulums that can support sensitivities below 10−19Nm/√Hz, while the motion of the pendulums are dominated by quantum radiation pressure noise at sub-microwatts of incoming laser power. These developments will provide horizons for experiments at the interface of quantum mechanics and gravity.},
  author       = {Agafonova, Sofya and Mishra, Umang and Diorico, Fritz R and Hosten, Onur},
  issn         = {2643-1564},
  journal      = {Physical Review Research},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Zigzag optical cavity for sensing and controlling torsional motion}},
  doi          = {10.1103/physrevresearch.6.013141},
  volume       = {6},
  year         = {2024},
}

@phdthesis{17225,
  abstract     = {This thesis describes the development of an atom interferometer designed to exploit the
advantages of utilizing quantum entanglement for enhanced precision measurements beyond
the standard quantum limit. While the project remains ongoing, significant progress has been
made.
A key contribution of this work is the development of Quantrol, an experimental control
system leveraging the ARTIQ framework. This software enables precise timing and control
without requiring prior knowledge of ARTIQ’s implementation details or coding experience.
The interface offers user friendly visual comprehension of the experimental sequence and
extended capabilities, allowing researchers to scan variables with a simple click of a mouse.
The main proposed project is to implement atom interferometric sequence with squeezed input
states inside of a dipole trap generated by a high finesse cavity. The presence of the dipole
trap allows one dimensional atomic cloud split while maintaining relatively strong confinement
in other directions.
We are currently able to trap and cool 87Rb atoms to few micro kelvin temperatures, load
them into the dipole trap and state prepare them to be used for squeezing and interferometric
sequence.},
  author       = {Li, Vyacheslav},
  issn         = {2663-337X},
  pages        = {79},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Towards a quantum entanglement enhanced atom interferomter}},
  doi          = {10.15479/at:ista:17225},
  year         = {2024},
}

@article{13233,
  abstract     = {We study the impact of finite-range physics on the zero-range-model analysis of three-body recombination in ultracold atoms. We find that temperature dependence of the zero-range parameters can vary from one set of measurements to another as it may be driven by the distribution of error bars in the experiment, and not by the underlying three-body physics. To study finite-temperature effects in three-body recombination beyond the zero-range physics, we introduce and examine a finite-range model based upon a hyperspherical formalism. The systematic error discussed in this Letter may provide a significant contribution to the error bars of measured three-body parameters.},
  author       = {Agafonova, Sofya and Lemeshko, Mikhail and Volosniev, Artem},
  issn         = {2469-9934},
  journal      = {Physical Review A},
  number       = {6},
  publisher    = {American Physical Society},
  title        = {{Finite-range bias in fitting three-body loss to the zero-range model}},
  doi          = {10.1103/PhysRevA.107.L061304},
  volume       = {107},
  year         = {2023},
}

@article{14749,
  abstract     = {We unveil a powerful method for the stabilization of laser injection locking based on sensing variations in the output beam ellipticity of an optically seeded laser. The effect arises due to an interference between the seeding beam and the injected laser output. We demonstrate the method for a commercial semiconductor laser without the need for any internal changes to the readily operational injection locked laser system that was used. The method can also be used to increase the mode-hop free tuning range of lasers, and has the potential to fill a void in the low-noise laser industry.},
  author       = {Mishra, Umang and Li, Vyacheslav and Wald, Sebastian and Agafonova, Sofya and Diorico, Fritz R and Hosten, Onur},
  issn         = {1539-4794},
  journal      = {Optics Letters},
  keywords     = {Atomic and Molecular Physics, and Optics},
  number       = {15},
  pages        = {3973--3976},
  publisher    = {Optica Publishing Group},
  title        = {{Monitoring and active stabilization of laser injection locking using beam ellipticity}},
  doi          = {10.1364/ol.495553},
  volume       = {48},
  year         = {2023},
}

@article{13264,
  abstract     = {We build a parametric amplifier with a Josephson field-effect transistor (JoFET) as the active element. The resonant frequency of the device is field-effect tunable over a range of 2 GHz. The JoFET amplifier has 20 dB of gain, 4 MHz of instantaneous bandwidth, and a 1-dB compression point of -125.5 dBm when operated at a fixed resonance frequency.

},
  author       = {Phan, Duc T and Falthansl-Scheinecker, Paul and Mishra, Umang and Strickland, W. M. and Langone, D. and Shabani, J. and Higginbotham, Andrew P},
  issn         = {2331-7019},
  journal      = {Physical Review Applied},
  number       = {6},
  publisher    = {American Physical Society},
  title        = {{Gate-tunable superconductor-semiconductor parametric amplifier}},
  doi          = {10.1103/PhysRevApplied.19.064032},
  volume       = {19},
  year         = {2023},
}

@article{14759,
  abstract     = {Proper operation of electro-optic I/Q modulators relies on precise adjustment and control of the relative phase biases between the modulator’s internal interferometer arms. We present an all-analog phase bias locking scheme where error signals are obtained from the beat between the optical carrier and optical tones generated by an auxiliary 2 MHz 𝑅𝐹 tone to lock the phases of all three involved interferometers for operation up to 10 GHz. With the developed method, we demonstrate an I/Q modulator in carrier-suppressed single-sideband mode, where the suppressed carrier and sideband are locked at optical power levels <−27dB
 relative to the transmitted sideband. We describe a simple analytical model for calculating the error signals and detail the implementation of the electronic circuitry for the implementation of the method.},
  author       = {Wald, Sebastian and Diorico, Fritz R and Hosten, Onur},
  issn         = {2155-3165},
  journal      = {Applied Optics},
  keywords     = {Atomic and Molecular Physics, and Optics, Engineering (miscellaneous), Electrical and Electronic Engineering},
  number       = {1},
  pages        = {1--7},
  publisher    = {Optica Publishing Group},
  title        = {{Analog stabilization of an electro-optic I/Q modulator with an auxiliary modulation tone}},
  doi          = {10.1364/ao.474118},
  volume       = {62},
  year         = {2023},
}

@article{10652,
  abstract     = {Finding a feasible scheme for testing the quantum mechanical nature of the gravitational interaction has been attracting an increasing level of attention. Gravity mediated entanglement generation so far appears to be the key ingredient for a potential experiment. In a recent proposal [D. Carney et al., PRX Quantum 2, 030330 (2021)] combining an atom interferometer with a low-frequency mechanical oscillator, a coherence revival test is proposed for verifying this entanglement generation. With measurements performed only on the atoms, this protocol bypasses the need for correlation measurements. Here, we explore formulations of such a protocol, and specifically find that in the envisioned regime of operation with high thermal excitation, semiclassical models, where there is no concept of entanglement, also give the same experimental signatures. We elucidate in a fully quantum mechanical calculation that entanglement is not the source of the revivals in the relevant parameter regime. We argue that, in its current form, the suggested test is only relevant if the oscillator is nearly in a pure quantum state, and in this regime the effects are too small to be measurable. We further discuss potential open ends. The results highlight the importance and subtleties of explicitly considering how the quantum case differs from the classical expectations when testing for the quantum mechanical nature of a physical system.},
  author       = {Hosten, Onur},
  issn         = {2643-1564},
  journal      = {Physical Review Research},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Constraints on probing quantum coherence to infer gravitational entanglement}},
  doi          = {10.1103/PhysRevResearch.4.013023},
  volume       = {4},
  year         = {2022},
}

@article{11438,
  abstract     = {Lasers with well-controlled relative frequencies are indispensable for many applications in science and technology. We present a frequency-offset locking method for lasers based on beat-frequency discrimination utilizing hybrid electronic LC filters. The method is specifically designed for decoupling the tightness of the lock from the broadness of its capture range. The presented demonstration locks two free-running diode lasers at 780 nm with a 5.5-GHz offset. It displays an offset frequency instability below 55 Hz for time scales in excess of 1000 s and a minimum of 12 Hz at 10-s averaging. The performance is complemented with a 190-MHz lock-capture range, a tuning range of up to 1 GHz, and a frequency ramp agility of 200kHz/μs.},
  author       = {Li, Vyacheslav and Diorico, Fritz R and Hosten, Onur},
  issn         = {2331-7019},
  journal      = {Physical Review Applied},
  keywords     = {General Physics and Astronomy},
  number       = {5},
  publisher    = {American Physical Society},
  title        = {{Laser frequency-offset locking at 10-Hz-level instability using hybrid electronic filters}},
  doi          = {10.1103/physrevapplied.17.054031},
  volume       = {17},
  year         = {2022},
}

@article{9331,
  abstract     = {Quantum entanglement has been generated and verified in cold-atom experiments and used to make atom-interferometric measurements below the shot-noise limit. However, current state-of-the-art cold-atom devices exploit separable (i.e., unentangled) atomic states. This perspective piece asks the question: can entanglement usefully improve cold-atom sensors, in the sense that it gives new sensing capabilities unachievable with current state-of-the-art devices? We briefly review the state-of-the-art in precision cold-atom sensing, focusing on clocks and inertial sensors, identifying the potential benefits entanglement could bring to these devices, and the challenges that need to be overcome to realize these benefits. We survey demonstrated methods of generating metrologically useful entanglement in cold-atom systems, note their relative strengths and weaknesses, and assess their prospects for near-to-medium term quantum-enhanced cold-atom sensing.},
  author       = {Szigeti, Stuart S. and Hosten, Onur and Haine, Simon A.},
  issn         = {0003-6951},
  journal      = {Applied Physics Letters},
  number       = {14},
  publisher    = {AIP Publishing},
  title        = {{Improving cold-atom sensors with quantum entanglement: Prospects and challenges}},
  doi          = {10.1063/5.0050235},
  volume       = {118},
  year         = {2021},
}

@article{8285,
  abstract     = {We demonstrate the utility of optical cavity generated spin-squeezed states in free space atomic fountain clocks in ensembles of 390 000 87Rb atoms. Fluorescence imaging, correlated to an initial quantum nondemolition measurement, is used for population spectroscopy after the atoms are released from a confining lattice. For a free fall time of 4 milliseconds, we resolve a single-shot phase sensitivity of 814(61) microradians, which is 5.8(0.6) decibels (dB) below the quantum projection limit. We observe that this squeezing is preserved as the cloud expands to a roughly 200  μm radius and falls roughly 300  μm in free space. Ramsey spectroscopy with 240 000 atoms at a 3.6 ms Ramsey time results in a single-shot fractional frequency stability of 8.4(0.2)×10−12, 3.8(0.2) dB below the quantum projection limit. The sensitivity and stability are limited by the technical noise in the fluorescence detection protocol and the microwave system, respectively.},
  author       = {Malia, Benjamin K. and Martínez-Rincón, Julián and Wu, Yunfan and Hosten, Onur and Kasevich, Mark A.},
  issn         = {1079-7114},
  journal      = {Physical Review Letters},
  number       = {4},
  publisher    = {American Physical Society},
  title        = {{Free space Ramsey spectroscopy in rubidium with noise below the quantum projection limit}},
  doi          = {10.1103/PhysRevLett.125.043202},
  volume       = {125},
  year         = {2020},
}

@article{8319,
  abstract     = {We demonstrate that releasing atoms into free space from an optical lattice does not deteriorate cavity-generated spin squeezing for metrological purposes. In this work, an ensemble of 500000 spin-squeezed atoms in a high-finesse optical cavity with near-uniform atom-cavity coupling is prepared, released into free space, recaptured in the cavity, and probed. Up to ∼10 dB of metrologically relevant squeezing is retrieved for 700μs free-fall times, and decaying levels of squeezing are realized for up to 3 ms free-fall times. The degradation of squeezing results from loss of atom-cavity coupling homogeneity between the initial squeezed state generation and final collective state readout. A theoretical model is developed to quantify this degradation and this model is experimentally validated.},
  author       = {Wu, Yunfan and Krishnakumar, Rajiv and Martínez-Rincón, Julián and Malia, Benjamin K. and Hosten, Onur and Kasevich, Mark A.},
  issn         = {2469-9934},
  journal      = {Physical Review A},
  number       = {1},
  publisher    = {American Physical Society},
  title        = {{Retrieval of cavity-generated atomic spin squeezing after free-space release}},
  doi          = {10.1103/PhysRevA.102.012224},
  volume       = {102},
  year         = {2020},
}