%0 Journal Article %D 2023 %T Collision-resolved pressure sensing %A Daniel S. Barker %A Daniel Carney %A Thomas W. LeBrun %A David C. Moore %A Jacob M. Taylor %X

Heat and pressure are ultimately transmitted via quantized degrees of freedom, like gas particles and phonons. While a continuous Brownian description of these noise sources is adequate to model measurements with relatively long integration times, sufficiently precise measurements can resolve the detailed time dependence coming from individual bath-system interactions. We propose the use of nanomechanical devices operated with impulse readout sensitivity around the ``standard quantum limit'' to sense ultra-low gas pressures by directly counting the individual collisions of gas particles on a sensor. We illustrate this in two paradigmatic model systems: an optically levitated nanobead and a tethered membrane system in a phononic bandgap shield.

%8 3/17/2023 %G eng %U https://arxiv.org/abs/2303.09922 %0 Journal Article %J Phys. Rev. A %D 2023 %T Decoherence from Long-Range Forces in Atom Interferometry %A Jonathan Kunjummen %A Daniel Carney %A Jacob M. Taylor %B Phys. Rev. A %V 107 %8 3/17/2023 %G eng %U https://arxiv.org/abs/2205.03006 %N 033319 %R https://doi.org/10.1103/PhysRevA.107.033319 %0 Journal Article %D 2023 %T A general approach to backaction-evading receivers with magnetomechanical and electromechanical sensors %A Brittany Richman %A Sohitri Ghosh %A Daniel Carney %A Gerard Higgins %A Peter Shawhan %A C. J. Lobb %A Jacob M. Taylor %X

Today's mechanical sensors are capable of detecting extremely weak perturbations while operating near the standard quantum limit. However, further improvements can be made in both sensitivity and bandwidth when we reduce the noise originating from the process of measurement itself -- the quantum-mechanical backaction of measurement -- and go below this 'standard' limit, possibly approaching the Heisenberg limit. One of the ways to eliminate this noise is by measuring a quantum nondemolition variable such as the momentum in a free-particle system. Here, we propose and characterize theoretical models for direct velocity measurement that utilize traditional electric and magnetic transducer designs to generate a signal while enabling this backaction evasion. We consider the general readout of this signal via electric or magnetic field sensing by creating toy models analogous to the standard optomechanical position-sensing problem, thereby facilitating the assessment of measurement-added noise. Using simple models that characterize a wide range of transducers, we find that the choice of readout scheme -- voltage or current -- for each mechanical detector configuration implies access to either the position or velocity of the mechanical sub-system. This in turn suggests a path forward for key fundamental physics experiments such as the direct detection of dark matter particles.

%8 11/16/2023 %G eng %U https://arxiv.org/abs/2311.09587 %0 Journal Article %J Phys. Rev. A %D 2023 %T Shadow process tomography of quantum channels %A Jonathan Kunjummen %A Minh C. Tran %A Daniel Carney %A Jacob M. Taylor %X

Quantum process tomography is a critical capability for building quantum computers, enabling quantum networks, and understanding quantum sensors. Like quantum state tomography, the process tomography of an arbitrary quantum channel requires a number of measurements that scale exponentially in the number of quantum bits affected. However, the recent field of shadow tomography, applied to quantum states, has demonstrated the ability to extract key information about a state with only polynomially many measurements. In this work, we apply the concepts of shadow state tomography to the challenge of characterizing quantum processes. We make use of the Choi isomorphism to directly apply rigorous bounds from shadow state tomography to shadow process tomography, and we find additional bounds on the number of measurements that are unique to process tomography. Our results, which include algorithms for implementing shadow process tomography enable new techniques including evaluation of channel concatenation and the application of channels to shadows of quantum states. This provides a dramatic improvement for understanding large-scale quantum systems.

%B Phys. Rev. A %V 107 %8 4/4/2023 %G eng %U https://arxiv.org/abs/2110.03629 %N 042403 %R https://doi.org/10.1103/PhysRevA.107.042403 %0 Journal Article %D 2023 %T Strongly incoherent gravity %A Daniel Carney %A Jacob M. Taylor %X

While most fundamental interactions in nature are known to be mediated by quantized fields, the possibility has been raised that gravity may behave differently. Making this concept precise enough to test requires consistent models. Here we construct an explicit example of a theory where a non-entangling version of an arbitrary two-body potential V(r) arises from local measurements and feedback forces. While a variety of such theories exist, our construction causes particularly strong decoherence compared to more subtle approaches. Regardless, expectation values of observables obey the usual classical dynamics, while the interaction generates no entanglement. Applied to the Newtonian potential, this produces a non-relativistic model of gravity with fundamental loss of unitarity. The model contains a pair of free parameters, a substantial range of which is not excluded by observations to date. As an alternative to testing entanglement properties, we show that the entire remaining parameter space can be tested by looking for loss of quantum coherence in small systems like atom interferometers coupled to oscillating source masses.

%8 1/20/2023 %G eng %U https://arxiv.org/abs/2301.08378 %0 Journal Article %D 2021 %T Comment on "Using an atom interferometer to infer gravitational entanglement generation'' %A Daniel Carney %A Holger Müller %A Jacob M. Taylor %X

Our paper arXiv:2101.11629 contains a technical error which changes some of the conclusions. We thank Streltsov, Pedernales, and Plenio for bringing the essence of this error to our attention. Here we explain the error, examine its consequences, and suggest methods to overcome the resulting weakness in the proposed experiment.

%8 11/8/2021 %G eng %U https://arxiv.org/abs/2111.04667 %0 Journal Article %J PRX Quantum %D 2021 %T Faster Digital Quantum Simulation by Symmetry Protection %A Minh C. Tran %A Yuan Su %A Daniel Carney %A J. M. Taylor %X

Simulating the dynamics of quantum systems is an important application of quantum computers and has seen a variety of implementations on current hardware. We show that by introducing quantum gates implementing unitary transformations generated by the symmetries of the system, one can induce destructive interference between the errors from different steps of the simulation, effectively giving faster quantum simulation by symmetry protection. We derive rigorous bounds on the error of a symmetry-protected simulation algorithm and identify conditions for optimal symmetry protection. In particular, when the symmetry transformations are chosen as powers of a unitary, the error of the algorithm is approximately projected to the so-called quantum Zeno subspaces. We prove a bound on this approximation error, exponentially improving a recent result of Burgarth, Facchi, Gramegna, and Pascazio. We apply our technique to the simulations of the XXZ Heisenberg interactions with local disorder and the Schwinger model in quantum field theory. For both systems, our algorithm can reduce the simulation error by several orders of magnitude over the unprotected simulation. Finally, we provide numerical evidence suggesting that our technique can also protect simulation against other types of coherent, temporally correlated errors, such as the 1/f noise commonly found in solid-state experiments.

%B PRX Quantum %V 2 %8 2/14/2021 %G eng %U https://arxiv.org/abs/2006.16248 %9 Report number: FERMILAB-PUB-20-240-QIS-T %R http://dx.doi.org/10.1103/PRXQuantum.2.010323 %0 Journal Article %D 2021 %T Testing quantum gravity with interactive information sensing %A Daniel Carney %A Holger Müller %A Jacob M. Taylor %X

We suggest a test of a central prediction of perturbatively quantized general relativity: the coherent communication of quantum information between massive objects through gravity. To do this, we introduce the concept of interactive quantum information sensing, a protocol tailored to the verification of dynamical entanglement generation between a pair of systems. Concretely, we propose to monitor the periodic wavefunction collapse and revival in an atomic interferometer which is gravitationally coupled to a mechanical oscillator. We prove a theorem which shows that, under the assumption of time-translation invariance, this collapse and revival is possible if and only if the gravitational interaction forms an entangling channel. Remarkably, as this approach improves at moderate temperatures and relies primarily upon atomic coherence, our numerical estimates indicate feasibility with current devices.

%8 1/27/2021 %G eng %U https://arxiv.org/abs/2101.11629 %0 Journal Article %J Phys. Rev. Lett. %D 2021 %T Trapped electrons and ions as particle detectors %A Daniel Carney %A Hartmut Häffner %A David C. Moore %A J. M. Taylor %X

Electrons and ions trapped with electromagnetic fields have long served as important high-precision metrological instruments, and more recently have also been proposed as a platform for quantum information processing. Here we point out that these systems can also be used as highly sensitive detectors of passing charged particles, due to the combination of their extreme charge-to-mass ratio and low-noise quantum readout and control. In particular, these systems can be used to detect energy depositions many orders of magnitude below typical ionization scales. As an illustration, we show that current devices can be used to provide competitive sensitivity to models where ambient dark matter particles carry small electric millicharges ≪e. Our calculations may also be useful in the characterization of noise in quantum computers coming from backgrounds of charged particles.

%B Phys. Rev. Lett. %V 127 %8 8/5/2021 %G eng %U https://arxiv.org/abs/2104.05737 %N 061804 %R https://doi.org/10.1103/PhysRevLett.127.061804 %0 Journal Article %J New Journal of Physics %D 2021 %T Ultralight dark matter detection with mechanical quantum sensors %A Daniel Carney %A Anson Hook %A Zhen Liu %A J. M. Taylor %A Yue Zhao %X

We consider the use of quantum-limited mechanical force sensors to detect ultralight (sub-meV) dark matter candidates which are weakly coupled to the standard model. We show that mechanical sensors with masses around or below the milligram scale, operating around the standard quantum limit, would enable novel searches for dark matter with natural frequencies around the kHz scale. This would complement existing strategies based on torsion balances, atom interferometers, and atomic clock systems

%B New Journal of Physics %V 23 %P 023041 %8 3/10/2021 %G eng %U https://arxiv.org/abs/1908.04797 %N 2 %R https://doi.org/10.1088/1367-2630/abd9e7 %0 Journal Article %J Phys. Rev. A %D 2020 %T Back-action evading impulse measurement with mechanical quantum sensors %A Sohitri Ghosh %A Daniel Carney %A Peter Shawhan %A J. M. Taylor %X

The quantum measurement of any observable naturally leads to noise added by the act of measurement. Approaches to evade or reduce this noise can lead to substantial improvements in a wide variety of sensors, from laser interferometers to precision magnetometers and more. In this paper, we develop a measurement protocol based upon pioneering work by the gravitational wave community which allows for reduction of added noise from measurement by coupling an optical field to the momentum of a small mirror. As a specific implementation, we present a continuous measurement protocol using a double-ring optomechanical cavity. We demonstrate that with experimentally-relevant parameters, this protocol can lead to significant back-action noise evasion, yielding measurement noise below the standard quantum limit over many decades of frequency.

%B Phys. Rev. A %V 102 %8 8/28/2020 %G eng %U https://arxiv.org/pdf/1910.11892.pdf %N 023525 %9 FERMILAB-PUB-19-537-T %R https://doi.org/10.1103/PhysRevA.102.023525 %0 Journal Article %J Phys. Rev. D %D 2020 %T Gravitational Direct Detection of Dark Matter %A Daniel Carney %A Sohitri Ghosh %A Gordan Krnjaic %A J. M. Taylor %X

The only coupling dark matter is guaranteed to have with the standard model is through gravity. Here we propose a concept for direct dark matter detection using only this gravitational coupling, enabling a new regime of detection. Leveraging dramatic advances in the ability to create, maintain, and probe quantum states of massive objects, we suggest that an array of quantum-limited impulse sensors may be capable of detecting the correlated gravitational force created by a passing dark matter particle. We present two concrete realizations of this scheme, using either mechanical resonators or freely-falling masses. With currently available technology, a meter-scale apparatus of this type could detect any dark matter candidate around the Planck mass or heavier.

%B Phys. Rev. D %V 102 %8 10/13/2020 %G eng %U https://arxiv.org/abs/1903.00492 %N 072003 %9 FERMILAB-PUB-19-082-AE-T %R https://doi.org/10.1103/PhysRevD.102.072003 %0 Journal Article %J Bulletin of the American Physical Society %D 2020 %T Position Space Decoherence From Long-Range Interaction With Background Gas %A Jonathan Kunjummen %A Daniel Carney %A J. M. Taylor %X

 Experiments in matter wave interferometry and optomechanics are increasing the spatial extent of wavefunctions of massive quantum systems; this gives rise to new sources of decoherence that must be characterized. Here we calculate the position space decoherence of a quantum particle due to interaction with a fluctuating classical background gas for several different force laws. We begin with the calculation of this effect for the Newton potential. To our knowledge, this calculation has not been done before. We then solve the same problem in the case of a Yukawa interaction, which interpolates between our long-range force result and the well-studied formula for collisional decoherence from a contact interaction. Unlike the contact interaction case, where the decoherence rate becomes independent of distance for large quantum particle separations, we observe that a long-range interaction leads to quadratic scaling of the decoherence rate with distance even at large separations. This work is relevant to the generation of massive superposition in optomechanical and atom beam experiments, and to conclude we comment on the use of this decoherence signal for gravitational detection of dark matter. 

%B Bulletin of the American Physical Society %8 06/05/2020 %G eng %U http://meetings.aps.org/Meeting/DAMOP20/Session/S08.5 %9 Invited paper of the DAMOP20 Meeting of The American Physical Society %0 Journal Article %J Phys. Rev. Lett. %D 2020 %T Search for composite dark matter with optically levitated sensors %A Fernando Monteiro %A Gadi Afek %A Daniel Carney %A Gordan Krnjaic %A Jiaxiang Wang %A David C. Moore %X

Results are reported from a search for a class of composite dark matter models with feeble, long-range interactions with normal matter. We search for impulses arising from passing dark matter particles by monitoring the mechanical motion of an optically levitated nanogram mass over the course of several days. Assuming such particles constitute the dominant component of dark matter, this search places upper limits on their interaction with neutrons of αn≤1.2×10−7 at 95\% confidence for dark matter masses between 1--10 TeV and mediator masses mφ≤0.1 eV. Due to the large enhancement of the cross-section for dark matter to coherently scatter from a nanogram mass (∼1029 times that for a single neutron) and the ability to detect momentum transfers as small as ∼200 MeV/c, these results provide sensitivity to certain classes of composite dark matter models that substantially exceeds existing searches, including those employing kg-scale or ton-scale targets. Extensions of these techniques can enable directionally-sensitive searches for a broad class of previously inaccessible heavy dark matter candidates. 

%B Phys. Rev. Lett. %V 125 %8 11/2/2020 %G eng %U https://arxiv.org/abs/2007.12067 %N 181102 %R https://doi.org/10.1103/PhysRevLett.125.181102 %0 Journal Article %J High Energ. Phys. %D 2018 %T On the need for soft dressing %A Daniel Carney %A Laurent Chaurette %A Dominik Neuenfeld %A Gordon Semenoff %X

In order to deal with IR divergences arising in QED or perturbative quantum gravity scattering processes, one can either calculate inclusive quantities or use dressed asymptotic states. We consider incoming superpositions of momentum eigenstates and show that in calculations of cross-sections these two approaches yield different answers: in the inclusive formalism no interference occurs for incoming finite superpositions and wavepackets do not scatter at all, while the dressed formalism yields the expected interference terms. This suggests that rather than Fock space states, one should use Faddeev-Kulish-type dressed states to correctly describe physical processes involving incoming superpositions. We interpret this in terms of selection rules due to large U(1) gauge symmetries and BMS supertranslations.

%B High Energ. Phys. %V 121 %8 2018 %G eng %0 Journal Article %J Phys. Rev. %D 2018 %T Structure of Correlated Worldline Theories of Quantum Gravity %A Andrei O. Barvinsky %A Daniel Carney %A Philip C. E. Stamp %X

We consider the general form of "Correlated Worldline" (CWL) theories of quantum gravity. We show that one can have 2 different kinds of CWL theory, in which the generating functional is written as either a sum or a product over multiple copies of the coupled matter and gravitational fields. In both versions, the paths in a functional formulation are correlated via gravity itself, causing a breakdown of the superposition principle; however, the product form survives consistency tests not satisfied by the summed form. To better understand the structure of these two theories, we show how to perform diagrammatic expansions in the gravitational coupling for each version of CWL theory, using particle propagation and scalar fields as examples. We explicitly calculate contributions to 2-point and 4-point functions, again for each version of the theory, up to 2nd-order in the gravitational coupling.

%B Phys. Rev. %V D %P 084052 %8 2018/06/21 %G eng %U https://arxiv.org/abs/1806.08043 %N 98 %R https://doi.org/10.1103/PhysRevD.98.084052 %0 Journal Article %D 2018 %T Tabletop experiments for quantum gravity: a user's manual %A Daniel Carney %A Philip C. E. Stamp %A J. M. Taylor %X

Recent advances in cooling, control, and measurement of mechanical systems in the quantum regime have opened the possibility of the first direct observation of quantum gravity, at scales achievable in experiments. This paper gives a broad overview of this idea, using some matter-wave and optomechanical systems to illustrate the predictions of a variety of models of low-energy quantum gravity. We first review the treatment of perturbatively quantized general relativity as an effective quantum field theory, and consider the particular challenges of observing quantum effects in this framework. We then move on to a variety of alternative models, such as those in which gravity is classical, emergent, or responsible for a breakdown of quantum mechanics.

%G eng %U https://arxiv.org/abs/1807.11494 %0 Journal Article %D 2018 %T Tabletop experiments for quantum gravity: a user's manual %A Daniel Carney %A Philip C. E. Stamp %A J. M. Taylor %X

Recent advances in cooling, control, and measurement of mechanical systems in the quantum regime have opened the possibility of the first direct observation of quantum gravity, at scales achievable in experiments. This paper gives a broad overview of this idea, using some matter-wave and optomechanical systems to illustrate the predictions of a variety of models of low-energy quantum gravity. We first review the treatment of perturbatively quantized general relativity as an effective quantum field theory, and consider the particular challenges of observing quantum effects in this framework. We then move on to a variety of alternative models, such as those in which gravity is classical, emergent, or responsible for a breakdown of quantum mechanics.

%G eng %U https://arxiv.org/abs/1807.11494