Quantum technologies: an old new story

Georgescu, Iulia; Nori, Franco

doi:10.1088/2058-7058/25/05/28

Cited by 39 publications

(28 citation statements)

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“…Using stimulated Raman transitions between ground hyperfine states, 12 cycles of the interferometer sequence cool a freely-moving atom cloud from 21 µK to 3 µK. This pulsed analog of continuous-wave Doppler cooling is effective at temperatures down to the recoil limit; with augmentation pulses to increase the interferometer area, it should cool more quickly than conventional methods, and be more suitable for species that lack a closed radiative transition.The laser cooling of atomic gases has revolutionized experimental atomic physics [1] and raised the prospect of a range of atomic quantum technologies [2,3]. However, traditional Doppler cooling [4,5] relies upon the velocity-dependence of a single narrow radiative transition, and spontaneous emission to reset the atomic state.…”

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Interferometric Laser Cooling of Atomic Rubidium

et al. 2015

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We report the 1-D cooling of 85 Rb atoms using a velocity-dependent optical force based upon Ramsey matter-wave interferometry. Using stimulated Raman transitions between ground hyperfine states, 12 cycles of the interferometer sequence cool a freely-moving atom cloud from 21 µK to 3 µK. This pulsed analog of continuous-wave Doppler cooling is effective at temperatures down to the recoil limit; with augmentation pulses to increase the interferometer area, it should cool more quickly than conventional methods, and be more suitable for species that lack a closed radiative transition.The laser cooling of atomic gases has revolutionized experimental atomic physics [1] and raised the prospect of a range of atomic quantum technologies [2,3]. However, traditional Doppler cooling [4,5] relies upon the velocity-dependence of a single narrow radiative transition, and spontaneous emission to reset the atomic state. The cooling force is limited to a half photon-impulse per excited-state lifetime and, as many impulses are needed, requires a transition that can be closed by a few repump lasers. Doppler cooling has thus so far been limited to a handful of atomic elements and molecules [6][7][8][9].In [10], Weitz and Hänsch proposed a mechanism that could extend laser cooling to a wider range of species, by replacing the continuous wave (CW) excitation of conventional Doppler cooling with the broadband laser pulses of Ramsey matter-wave interferometry, and interleaving inversion pulses to eliminate the dependence upon the internal state energies. The interference signal, and hence the impulse imparted, were thus determined only by the particle's kinetic energy; manifold transitions could be accessed and, while spontaneous emission remained the entropy-removing mechanism, various schemes [11][12][13] could increase the impulse per spontaneous event. With a drive towards efficient pulsed schemes for molecular cooling [14][15][16] supported by improved mode-locked laser technologies, interferometric cooling appears a promising and flexible tool.The idea of a pulsed Ramsey analog to CW Doppler cooling has until now remained untested. In this letter, we report the first experimental demonstration of 1-D interferometric cooling of a cloud of already ultracold Rb atoms. Our long-lived quasi-two-level system, comprising the two 5S 1/2 ground hyperfine states of 85 Rb between which we drive stimulated Raman transitions, in principle allows cooling to the recoil limit, and we show that with just 12 cycles of the interferometric cooling sequence the atom cloud is cooled from 21 ± 2 µK to 3.2 ± 0.4 µK. Relaxation after each cycle is achieved by rapid pumping and decay of the single-photon 5S 1/2 -5P 3/2 transition, and the cooling rate is therefore limited mainly by the time needed for interferometric resolution of the different velocity classes.The Raman interferometric cooling mechanism is as follows. Two π/2 laser pulses, separated by a dwell time τ , act upon a two-level atom |Ψ = c 1 |1 + c 2 |2 as the beamsplitter and combiner of a R...

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confidence: 99%

“…The laser cooling of atomic gases has revolutionized experimental atomic physics [1] and raised the prospect of a range of atomic quantum technologies [2,3]. However, traditional Doppler cooling [4,5] relies upon the velocity-dependence of a single narrow radiative transition, and spontaneous emission to reset the atomic state.…”

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confidence: 99%

Interferometric Laser Cooling of Atomic Rubidium

et al. 2015

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“…Such set of theoretical tools will be useful not just for applications to quantum computing, but in a wider field of quantum engineering and second-generation quantum technologies [34]. Moreover, it may prove indispensable when addressing problems such as quantum simulations [35,36], quantum-to-classical transition in open systems [37] and the challenging new field of quantum biology [38].…”

Section: The Problem and Possible Solutionsmentioning

confidence: 99%

How to test the â€œquantumnessâ€ of a quantum computer?

Zagoskin¹,

Il’ichev²,

Grajcar³

et al. 2014

Front. Physics

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Recent devices, using hundreds of superconducting quantum bits, claim to perform quantum computing. However, it is not an easy task to determine and quantify the degree of quantum coherence and control used by these devices. Namely, it is a difficult task to know with certainty whether or not a given device (e.g., the D-Wave One or D-Wave Two) is a quantum computer. Such a verification of quantum computing would be more accessible if we already had some kind of working quantum computer, to be able to compare the outputs of these various computing devices. Moreover, the verification process itself could strongly depend on whether the tested device is a standard (gate-based) or, e.g., an adiabatic quantum computer. Here we do not propose a technical solution to this quantum-computing "verification problem," but rather outline the problem in a way which would help both specialists and non-experts to see the scale of this difficult task, and indicate some possible paths toward its solution.Keywords: quantum computing, adiabatic quantum computing, quantum coherence, quantum annealing, D-Wave Systems, quantum simulations, quantum speed-up Suppose we are given a black box and told that this is a quantum computer. How do we test if it is capable of performing quantum computing? The standard approach would be to run a series of tests of few-qubit operations, and compare the outputs with results obtained using a standard (classical) computer simulating the quantum evolution. This is possible for small-size systems, likely comprising less than 40-50 qubits, given the current capabilities and fundamental limitations of classical computers (due to the exponential growth of computing resources needed to model large quantum systems [11]. But what if the system size is larger? Another challenging task would be to find out how to change the design of the "black-box computer" to improve its performance. Namely, if the black box computer is not working as a quantum computer, how to find this out and how to fix the problem?Now we are facing a similar situation. The development of an "adiabatic quantum annealer" by D-Wave Systems Inc. over the last few years did produce reactions ranging from excitement to skepticism [2][3][4][5][6][7][8][9]. Considerable interest was generated by:(1) the demonstration of quantum annealing in an 8-qubit register of the prototype processor [10]; (2) the sale of a 128-qubit quantum annealer "D-Wave One"to Lockheed Martin and its installation at the University of Southern California (2011), and its upgrade to a 512-qubit "D-Wave Two" (2013); (3) the subsequent evidence of quantum annealing in the working 108 qubits of this device [11,12]; (4) the realization of a quantum adiabatic algorithm on a nominally 512-qubit (439 qubits operational) device "D-Wave Two" outperforming at least some classical algorithms [13] and losing to some other classical algorithms Questions were raised concerning the relative speed of the D-Wave processors compared to classical optimization algorithms [7] and the quantum char...

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“…(57) can be extended to multiqubit networks [63] to study many-body physical phenomena, such as quantum entanglement and correlations.…”

Section: B Example: Non-markovian Qubit Network In Superconducting mentioning

confidence: 99%

Non-Markovian quantum input-output networks

Zhang

Liu

et al. 2013

Phys. Rev. A

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Quantum input-output response analysis is a useful method for modeling the dynamics of complex quantum networks, such as those for communication or quantum control via cascade connections. Non-Markovian effects are expected to be important in networks realized using mesoscopic circuits, but such effects have not yet been studied. Here we extend the Markovian input-output network formalism to non-Markovian networks. The general formalism can be applied to various examples: (i) we show how non-Markovian coherent feedback can reduce the speed of decoherence for an atom in an optical cavity; (ii) we examine the effect of finite-cavity bandwidths in a superconducting circuit.

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Quantum technologies: an old new story

Cited by 39 publications

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Interferometric Laser Cooling of Atomic Rubidium

Interferometric Laser Cooling of Atomic Rubidium

How to test the â€œquantumnessâ€ of a quantum computer?

Non-Markovian quantum input-output networks

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Quantum technologies: an old new story

Cited by 39 publications

References 0 publications

Interferometric Laser Cooling of Atomic Rubidium

Interferometric Laser Cooling of Atomic Rubidium

How to test the â€œquantumnessâ€ of a quantum computer?

Non-Markovian quantum input-output networks

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How to test the â€œquantumnessâ€ of a quantum computer?