Deterministic Squeezed States with Collective Measurements and Feedback

Cox, Karen; Greve, Graham P.; Weiner, Joshua M.; Thompson, James K.

doi:10.1103/physrevlett.116.093602

Cited by 211 publications

(204 citation statements)

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“…They are, however, not capable of generating spin squeezing needed to lower the projection noise. In contrast, dispersive measurements based upon off-resonant atom-light interactions enabled experimental demonstration of 18-20-dB spin squeezing [25,26]. These experiments used high-finesse optical cavities to achieve strong atom-light interaction with low atom numbers, and require significant technical effort to stabilize to sufficient robustness.…”

Section: Introductionmentioning

confidence: 99%

Dispersive detection of radio-frequency-dressed states

et al. 2018

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We introduce a method to dispersively detect alkali-metal atoms in radio-frequency-dressed states. In particular, we use dressed detection to measure populations and population differences of atoms prepared in their clock states. Linear birefringence of the atomic medium enables atom number detection via polarization homodyning, a form of common path interferometry. In order to achieve low technical noise levels, we perform optical sideband detection after adiabatic transformation of bare states into dressed states. The balanced homodyne signal then oscillates independently of field fluctuations at twice the dressing frequency, thus allowing for robust, phase-locked detection that circumvents low-frequency noise. Using probe pulses of two optical frequencies, we can detect both clock states simultaneously and obtain population difference as well as the total atom number. The scheme also allows for difference measurements by direct subtraction of the homodyne signals at the balanced detector, which should technically enable quantum noise limited measurements with prospects for the preparation of spin squeezed states. The method extends to other Zeeman sublevels and can be employed in a range of atomic clock schemes, atom interferometers, and other experiments using dressed atoms.

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Section: Introductionmentioning

confidence: 99%

Dispersive detection of radio-frequency-dressed states

et al. 2018

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“…Note that the mean spin and the variance are normalized to the value obtained for the |CSS . This corresponds to the procedure typically employed in the experiments [24,29,30]. As evident from the plot, the dashed black line which is obtained for symmetric probing of the atomic ensemble significantly differs from the present case.…”

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confidence: 44%

“…Measuring that the noise is squeezed below a certain bound is then a sufficient criterion for proving entanglement [11][12][13][14][15][16][17][18][19]. Due to the simplicity of this approach, it has been employed to show even multi-partite entanglement in a wide range of experiments [20][21][22][23][24]. However, an inherent assumption in the entanglement criteria based on spin squeezing is that all particles are probed with equal strength.…”

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confidence: 99%

Multipartite entanglement detection with nonsymmetric probing

et al. 2017

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We show that spin squeezing criteria commonly used for entanglement detection can be erroneous, if the probe is not symmetric. We then derive a lower bound on squeezing for separable states in spin systems probed asymmetrically. Using this we further develop a procedure that allows us to verify the degree of entanglement of a quantum state in the spin system. Finally, we apply our method for entanglement verification to existing experimental data, and use it to prove the existence of tri-partite entanglement in a spin squeezed atomic ensemble.Entanglement is a fundamental resource for proving nonclassicality of nature, and is a key feature for developing quantum technologies. It was first used experimentally for proving the breakdown of local realism [1,2], and has now become a practical ingredient in quantum information science and metrology [3]. As such, it is crucial to discern between separable and entangled systems. Unfortunately, this is not always straightforward; even though several criteria exist [4][5][6], it may be hard to experimentally verify that a state is entangled. Hence, there is a need for simple, practical procedures for proving that a system is entangled. An example of such a criterion is spin squeezing [7][8][9], which has often been used to probe entanglement in multi-particle systems [10]. One of its major advantages is that it relies on measuring only two observables: the mean spin and the fluctuations perpendicular to it. This makes it ideally suited for systems where complete control over all degrees of freedom is hard to achieve. Measuring that the noise is squeezed below a certain bound is then a sufficient criterion for proving entanglement [11][12][13][14][15][16][17][18][19]. Due to the simplicity of this approach, it has been employed to show even multi-partite entanglement in a wide range of experiments [20][21][22][23][24]. However, an inherent assumption in the entanglement criteria based on spin squeezing is that all particles are probed with equal strength. In many practical situations this is a very good approximation [21,23], but in others this is far from reality. As an example, consider a Gaussian beam probing a collection of trapped atoms. If the waist of the laser beam is much smaller than the size of the cloud, the atoms will have an asymmetric interaction with the light. This asymmetry leads to minor modifications of the interaction dynamics if suitable weighted operators are introduced [25,26]. For entanglement detection in the ensemble, however, the effect of such asymmetry may be much more severe and has so far not been investigated.In this article, we consider the effect of asymmetric probing on the entanglement criteria. We first consider a simple generalization of the standard squeezing criterion and show that it is no longer a suitable method for verifying entanglement. To overcome this problem we develop new entanglement criteria, that can accommodate the asymmetric probing of the particles. We show that our criteria are sufficient for detection of bi-partite...

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“…Secondly, building on the capability of quantum feedback reported in chapter 3, feedback is used to distil quantum correlations without destroying them. Feedback control of a mechanical oscillator thus joins the exclusive collective of a handful of platforms where manipulation of non-classical resources using feedback has been demonstrated [266,[328][329][330]. Finally, the fundamental limit of linear feedback control is elucidated: feedback, though capable of suppressing in-loop measurement back-action, is limited by quantum fluctuations amplified by the in-loop detector.…”

Section: Resultsmentioning

confidence: 99%

Quantum Limits on Measurement and Control of a Mechanical Oscillator

Sudhir

2018

Springer Theses

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PAR Vivishek SUDHIR JOSEPH CONRAD, Heart of DarknessExperimental physics demands a certain degree of manual dexterity, the patience to tolerate the mundane, and an inexhaustible supply of optimism. Tobias hired me to work on an immensely sophisticated experiment despite any proof of my possessing these qualities; I am indebted to him for the belief he has placed in me. I would also like to acknowledge his dedication to fostering an environment where the pursuit of science is unencumbered by other worldly concerns. Stefan, Ewold and Samuel bore the brunt of a theorist trying to perform delicate experiments; the stern, yet encouraging, stewardship of this trio ensured that I enjoyed the culture shock. Dal Wilson was more than a colleague and a post-doc; his pragmatic approach to physics provided the ideal counter-point in our attempts to forge a deeper understanding of things ranging from vibration isolation to the subtleties of quantum mechanics. Without the patient efforts of Amir, Ryan and Hendrik in designing, fabricating, and testing of devices, none of the results reported here would have been possible. I hope I have been able to bequeath a better vision of the future of our experiment to Sergey. Conversations with Alexey, Daniel and Nathan have enabled me to vicariously learn how to measure microwave "photons". John Jost once taught me how to decorate a Christmas tree; since then he has imparted some wisdom on frequency metrology, and some on atomic physics. Together with Dal, Victor and Caroline have probably spent the most time with me outside the lab; it was fun to exercise an air of social normalcy with this bunch. Christophe has been an amazing sparring partner on every subject capable of being brought under scientific scrutiny.The personal space required for the pursuit of science comes through the sacrifice of many people. My family back home in India -parents, sister, grand-parents -have had to patiently wait for the brief interludes when I go home. No words can do justice to this and the very many other pleasures they have surrendered over the years for my sake. Before physics attracted me, I was charmed by someone else; I am lucky to have married her. Long time friends, mentorsAjith and Subeesh -have played pivotal roles in my being able to engage in physics; I hope to repay this enormous debt, some day.It was a privilege to have learnt from a few great teachers during my formative years. Their vision of an indelible unity in nature continues to motivate my study of physics. vii AbstractThe precision measurement of position has a long-standing tradition in physics. Cavendish's verification of the universal law of gravitation using a torsion pendulum, Perrin's confirmation of the atomic hypothesis via the precise measurement of the Brownian motion, and, the verification of the mechanical effect of electromagnetic radiation, all belong to this classical heritage. Quantum mechanics posits that the measurement of position results in an uncertain momentum; an idea developed to full maturity within the ...

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Deterministic Squeezed States with Collective Measurements and Feedback

Cited by 211 publications

References 46 publications

Dispersive detection of radio-frequency-dressed states

Dispersive detection of radio-frequency-dressed states

Multipartite entanglement detection with nonsymmetric probing

Quantum Limits on Measurement and Control of a Mechanical Oscillator

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