Dynamic Stabilization of a Quantum Many-Body Spin System

Hoang, Thai M.; Gerving, Corey; Land, B. J.; Anquez, Martin; Hamley, C. D.; Chapman, Michael

doi:10.1103/physrevlett.111.090403

Cited by 58 publications

(59 citation statements)

References 40 publications

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“…We work within the physical F = 2 manifold because its associated nonlinearity g is one order of magnitude larger than for F = 1. Spurious processes out of the effective three level system are energetically suppressed by the quadratic Zeeman shift at a magnetic field of 0.9 G.The key feature of this three-mode implementation is that the nonlinear Hamiltonian can be tailored by controlling the phase and amplitude of this highly populated pump mode [11][12][13]: The effective nonlinear coupling strength κ is inverted by imprinting a phase shift of 2ϕ 0 = π, i.e., κ → e −i2ϕ0 κ = −κ, while its magnitude can be adjusted by the number of pump atoms.We can therefore experimentally realize a scheme that is divided into three building blocks: Entangled state preparation, interrogation, and nonlinear time reversal for readout [ Fig. 1(a)].…”

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confidence: 99%

“…The key feature of this three-mode implementation is that the nonlinear Hamiltonian can be tailored by controlling the phase and amplitude of this highly populated pump mode [11][12][13]: The effective nonlinear coupling strength κ is inverted by imprinting a phase shift of 2ϕ 0 = π, i.e., κ → e −i2ϕ0 κ = −κ, while its magnitude can be adjusted by the number of pump atoms.…”

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confidence: 99%

“…Thereby the spin-mixing dynamics is halted and the pump is energetically shifted effectively by 100 Hz [14]. We exploit this energy shift to imprint a dynamical phase of 2ϕ 0 = π onto the pump mode that changes the sign of the spin-changing collisions Hamiltonian [11]. This phase accumulation takes ∼ 2 ms. We then rapidly transfer the pump atoms back to |F = 2, m F = 0 and continue spin-changing collisions with identical coupling strength.…”

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Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

et al. 2016

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We experimentally demonstrate a nonlinear detection scheme exploiting time-reversal dynamics that disentangles continuous variable entangled states for feasible readout. Spin-exchange dynamics of Bose-Einstein condensates is used as the nonlinear mechanism which not only generates entangled states but can also be time reversed by controlled phase imprinting. For demonstration of a quantumenhanced measurement we construct an active atom SU(1,1) interferometer, where entangled state preparation and nonlinear readout both consist of parametric amplification. This scheme is capable of exhausting the quantum resource by detecting solely mean atom numbers. Controlled nonlinear transformations widen the spectrum of useful entangled states for applied quantum technologies.Nonlinear dynamics is the basis of generating nonclassical states of many particles. These entangled states are capable of improving a large variety of operations, e.g., computational tasks [1], communication and measurements [2]. Unlocking their full potential for quantum technologies requires both the generation and detection at the fundamental quantum limit. The generation of such highly entangled states with many particles has witnessed tremendous advances [3,4]. However, to fully exploit this quantum resource, the complete correlations on the single particle level need to be accessed, which still limits current experiments.To address this challenge, nonlinear readout schemes have been proposed [5][6][7][8]. Most of these employ a time inversion sequence. For this the nonlinear evolution that is used to produce the entangled state is inverted and reapplied for readout. If the state remains unperturbed, the second period of nonlinear evolution counteracts the first. This time-reversed readout disentangles the probe state such that the known separable initial state is recovered. This reversibility is nonperfect if the state is changed in between, similar to an incomplete Loschmidt-Echo [9]. By this sensitive mechanism, minute state perturbations are mapped onto readily discernable quantities.Experimentally, we use spin-changing collisions [10] in a mesoscopic spinor Bose-Einstein condensate. This nonlinear mechanism is the atomic analogue of parametric amplification, which is the textbook example of entangled state generation in quantum optics. At the same time, both the sign and the strength of the nonlinear coupling are experimentally adjustable, which makes this system ideally suited for realizing time reversal readout schemes.Spin exchange is performed in an effective three-level system within the spin F = 2 manifold of 87 Rb. For this the external degrees of freedom are frozen out such that dynamics is restricted to the spin degree of freedom. We start with a pure |F = 2, m F = 0 condensate (pump mode). Population in any m F = 0 state is carefully cleaned. During spin mixing atoms of the pump mode are coherently and pairwise scattered into the signal |↑ ≡ |2, 1 and idler |↓ ≡ |2, −1 mode, which we refer to as side modes (see Fig. 1). For small p...

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Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

et al. 2016

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“…Hj, 03.75.Mn, 67.85.Fg, 03.75.Kk A spinor Bose-Einstein condensate (BEC) is a multicomponent BEC with an additional spin degree of freedom, which has provided exciting opportunities to study quantum magnetism, superfluidity, strong correlations, spin-squeezing, and massive entanglement [1][2][3][4][5]. The interesting interactions in spinor BECs are interconversions among multiple spin states and magnetic field interactions (or microwave dressing field interactions) characterized by q net , the net quadratic Zeeman energy.…”

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Mapping the phase diagram of spinor condensates via adiabatic quantum phase transitions

et al. 2014

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We experimentally study two quantum phase transitions in a sodium spinor condensate immersed in a microwave dressing field. We also demonstrate that many previously unexplored regions in the phase diagram of spinor condensates can be investigated by adiabatically tuning the microwave field across one of the two quantum phase transitions. This method overcomes two major experimental challenges associated with some widely used methods, and is applicable to other atomic species. Agreements between our data and the mean-field theory for spinor Bose gases are also discussed.PACS numbers: 67.85. Hj, 03.75.Mn, 67.85.Fg, 03.75.Kk A spinor Bose-Einstein condensate (BEC) is a multicomponent BEC with an additional spin degree of freedom, which has provided exciting opportunities to study quantum magnetism, superfluidity, strong correlations, spin-squeezing, and massive entanglement [1][2][3][4][5]. The interesting interactions in spinor BECs are interconversions among multiple spin states and magnetic field interactions (or microwave dressing field interactions) characterized by q net , the net quadratic Zeeman energy. The interplay of these interactions leads to oscillations among multiple spin populations, which has been experimentally confirmed in F =123 Na spinor BECs [6][7][8][9][10][11][12], and in both F =1 and F =287 Rb spinor condensates [13][14][15][16][17].Several groups demonstrated the mean-field (MF) ground states of spinor BECs by holding BECs in a fixed magnetic field and letting spin population oscillations damp out over a few seconds [8][9][10][11]. The required damping time, determined by energy dissipation, may in some cases exceed the BEC lifetime. The exact mechanism involved in energy dissipation requires further study, although it has been shown that energy dissipates much faster in high magnetic fields [10]. For F =1 BECs, a magnetic field introduces only a positive q net , while a microwave field has a distinct advantage since it can induce both positive and negative q net [1,7,12,18,19]. As shown in Ref. [12], the same physics model explains spin-mixing dynamics observed in both microwave fields and magnetic fields. One would assume that, if given a long enough exposure to a microwave field, a spinor BEC could also reach its MF ground states. However, experimental studies on ground states of spinor BECs in microwave fields have proven to be very difficult, since these fields are created by near-resonant microwave pulses. Two major experimental challenges associated with microwave fields are atom losses and variations in magnetization m. Microwave-induced changes in both m and the atom number N can be detrimental, especially when a spinor BEC is exposed to a large microwave field for a prolonged time [7,12]. As a result, the phase diagram of F =1 BECs has not been well explored in the q net ≤ 0 region, where applying microwave fields may be necessary.In this paper, we demonstrate a new method to overcome the aforementioned experimental challenges and report the observation of two quantum phase ...

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“…Based on the topology of the mean-field phase portrait one can predict approximate quantum evolution and explain the squeezing mechanism of the initial separable state. This approach proved to be very useful in the study of spin-1/2 [16,[53][54][55][56] as well as spin-1 [5,[57][58][59] quantum systems.…”

Section: Reduction Of the Mean-field Phase Spacementioning

confidence: 99%

Spin squeezing in dipolar spinor condensates

Kajtoch

Witkowska

2016

Phys. Rev. A

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We study the effect of dipolar interactions on the level of squeezing in spin-1 Bose-Einstein condensates by using the single mode approximation. We limit our consideration to the su(2) Lie subalgebra spanned by spin operators. The biaxial nature of dipolar interactions allows for dynamical generation of spin-squeezed states in the system. We analyze the phase portraits in the reduced mean-filed space in order to determine positions of unstable fixed points. We calculate numerically spin squeezing parameter showing that it is possible to reach the strongest squeezing set by the two-axis countertwisting model. We partially explain scaling with the system size by using the Gaussian approach and the frozen spin approximation.

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Dynamic Stabilization of a Quantum Many-Body Spin System

Cited by 58 publications

References 40 publications

Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics

Mapping the phase diagram of spinor condensates via adiabatic quantum phase transitions

Spin squeezing in dipolar spinor condensates

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