01210nas a2200157 4500008004100000245004000041210003900081260001400120520077300134100002300907700001900930700002300949700002100972700002200993856003701015 2023 eng d00aCollision-resolved pressure sensing0 aCollisionresolved pressure sensing c3/17/20233 a

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.

1 aBarker, Daniel, S.1 aCarney, Daniel1 aLeBrun, Thomas, W.1 aMoore, David, C.1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2303.0992200422nas a2200133 4500008004100000245006200041210006100103260001400164490000800178100002400186700001900210700002200229856003700251 2023 eng d00aDecoherence from Long-Range Forces in Atom Interferometry0 aDecoherence from LongRange Forces in Atom Interferometry c3/17/20230 v1071 aKunjummen, Jonathan1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2205.0300602007nas a2200181 4500008004100000245010800041210006900149260001500218520141700233100002201650700001901672700001901691700002001710700001901730700001701749700002201766856003701788 2023 eng d00aA general approach to backaction-evading receivers with magnetomechanical and electromechanical sensors0 ageneral approach to backactionevading receivers with magnetomech c11/16/20233 a

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.

1 aRichman, Brittany1 aGhosh, Sohitri1 aCarney, Daniel1 aHiggins, Gerard1 aShawhan, Peter1 aLobb, C., J.1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2311.0958701610nas a2200157 4500008004100000245005000041210005000091260001300141490000800154520116900162100002401331700001901355700001901374700002201393856003701415 2023 eng d00aShadow process tomography of quantum channels0 aShadow process tomography of quantum channels c4/4/20230 v1073 a

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.

1 aKunjummen, Jonathan1 aTran, Minh, C.1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2110.0362901475nas a2200121 4500008004100000245003200041210003200073260001400105520115600119100001901275700002201294856003701316 2023 eng d00aStrongly incoherent gravity0 aStrongly incoherent gravity c1/20/20233 a

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.

1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2301.0837800790nas a2200133 4500008004100000245009400041210006900135260001400204520034000218100001900558700002000577700002200597856003700619 2021 eng d00aComment on "Using an atom interferometer to infer gravitational entanglement generation''0 aComment on Using an atom interferometer to infer gravitational e c11/8/20213 a

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.

1 aCarney, Daniel1 aMüller, Holger1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2111.0466701880nas a2200169 4500008004100000022001400041245006100055210006100116260001400177490000600191520140600197100001901603700001301622700001901635700001901654856003701673 2021 eng d a2691-339900aFaster Digital Quantum Simulation by Symmetry Protection0 aFaster Digital Quantum Simulation by Symmetry Protection c2/14/20210 v23 a

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.

1 aTran, Minh, C.1 aSu, Yuan1 aCarney, Daniel1 aTaylor, J., M. uhttps://arxiv.org/abs/2006.1624801340nas a2200133 4500008004100000245006500041210006500106260001400171520092300185100001901108700002001127700002201147856003701169 2021 eng d00aTesting quantum gravity with interactive information sensing0 aTesting quantum gravity with interactive information sensing c1/27/20213 a

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.

1 aCarney, Daniel1 aMüller, Holger1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2101.1162901337nas a2200157 4500008004100000245005300041210005300094260001300147490000800160520089300168100001901061700002201080700002101102700001901123856003701142 2021 eng d00aTrapped electrons and ions as particle detectors0 aTrapped electrons and ions as particle detectors c8/5/20210 v1273 a

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.

1 aCarney, Daniel1 aHäffner, Hartmut1 aMoore, David, C.1 aTaylor, J., M. uhttps://arxiv.org/abs/2104.0573701048nas a2200193 4500008004100000022001400041245006900055210006900124260001400193300001100207490000700218520051000225100001900735700001600754700001400770700001900784700001400803856003700817 2021 eng d a1367-263000aUltralight dark matter detection with mechanical quantum sensors0 aUltralight dark matter detection with mechanical quantum sensors c3/10/2021 a0230410 v233 a

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

1 aCarney, Daniel1 aHook, Anson1 aLiu, Zhen1 aTaylor, J., M.1 aZhao, Yue uhttps://arxiv.org/abs/1908.0479701337nas a2200157 4500008004100000245007600041210006900117260001400186490000800200520085400208100001901062700001901081700001901100700001901119856004101138 2020 eng d00aBack-action evading impulse measurement with mechanical quantum sensors0 aBackaction evading impulse measurement with mechanical quantum s c8/28/20200 v1023 a

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.

1 aGhosh, Sohitri1 aCarney, Daniel1 aShawhan, Peter1 aTaylor, J., M. uhttps://arxiv.org/pdf/1910.11892.pdf01216nas a2200157 4500008004100000245005000041210005000091260001500141490000800156520078000164100001900944700001900963700002000982700001901002856003701021 2020 eng d00aGravitational Direct Detection of Dark Matter0 aGravitational Direct Detection of Dark Matter c10/13/20200 v1023 a

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.

1 aCarney, Daniel1 aGhosh, Sohitri1 aKrnjaic, Gordan1 aTaylor, J., M. uhttps://arxiv.org/abs/1903.0049202249nas a2200133 4500008004100000245007900041210006900120260001500189520179100204100002401995700001902019700001902038856005802057 2020 eng d00aPosition Space Decoherence From Long-Range Interaction With Background Gas0 aPosition Space Decoherence From LongRange Interaction With Backg c06/05/20203 a

 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. 

1 aKunjummen, Jonathan1 aCarney, Daniel1 aTaylor, J., M. uhttp://meetings.aps.org/Meeting/DAMOP20/Session/S08.501697nas a2200181 4500008004100000245007000041210006900111260001400180490000800194520115900202100002301361700001501384700001901399700002001418700001901438700002101457856003701478 2020 eng d00aSearch for composite dark matter with optically levitated sensors0 aSearch for composite dark matter with optically levitated sensor c11/2/20200 v1253 a

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. 

1 aMonteiro, Fernando1 aAfek, Gadi1 aCarney, Daniel1 aKrnjaic, Gordan1 aWang, Jiaxiang1 aMoore, David, C. uhttps://arxiv.org/abs/2007.1206701248nas a2200157 4500008004100000245003400041210002700075260000900102490000800111520082700119100001900946700002300965700002300988700002101011856005801032 2018 eng d00aOn the need for soft dressing0 aneed for soft dressing c20180 v1213 a

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.

1 aCarney, Daniel1 aChaurette, Laurent1 aNeuenfeld, Dominik1 aSemenoff, Gordon uhttps://quics.umd.edu/publications/need-soft-dressing01396nas a2200157 4500008004100000245006600041210006600107260001500173300001100188490000600199520092600205100002601131700001901157700002501176856003701201 2018 eng d00aStructure of Correlated Worldline Theories of Quantum Gravity0 aStructure of Correlated Worldline Theories of Quantum Gravity c2018/06/21 a0840520 vD3 a

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.

1 aBarvinsky, Andrei, O.1 aCarney, Daniel1 aStamp, Philip, C. E. uhttps://arxiv.org/abs/1806.0804301154nas a2200121 4500008004100000245006200041210006000103520076900163100001900932700002500951700001900976856003700995 2018 eng d00aTabletop experiments for quantum gravity: a user's manual0 aTabletop experiments for quantum gravity a users manual3 a

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.

1 aCarney, Daniel1 aStamp, Philip, C. E.1 aTaylor, J., M. uhttps://arxiv.org/abs/1807.1149401154nas a2200121 4500008004100000245006200041210006000103520076900163100001900932700002500951700001900976856003700995 2018 eng d00aTabletop experiments for quantum gravity: a user's manual0 aTabletop experiments for quantum gravity a users manual3 a

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.

1 aCarney, Daniel1 aStamp, Philip, C. E.1 aTaylor, J., M. uhttps://arxiv.org/abs/1807.11494