Generation of Fock states in a superconducting quantum circuit

Hofheinz, M.; Weig, Eva M.; Ansmann, M.; Bialczak, Radoslaw C.; Lucero, Erik; Neeley, M.; O’Connell, A. D.; Wang, H.; Martinis, John M.; Cleland, A. N.

doi:10.1038/nature07136

Cited by 539 publications

(580 citation statements)

References 27 publications

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“…This anharmonicity has been observed with single atoms in both microwave 13 and optical cavities 14,15 . In circuit QED, this characteristic trait has been observed in time-domain measurements 16 . In a system similar to ours, the position of the n = 2 peaks was recently demonstrated in a two-tone pump-probe measurement 17 .…”

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confidence: 80%

Nonlinear response of the vacuum Rabi resonance

et al. 2008

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On the level of single atoms and photons, the coupling between atoms and the electromagnetic field is typically very weak. By using a cavity to confine the field, the strength of this interaction can be increased by many orders of magnitude, to a point where it dominates over any dissipative process. This strong-coupling regime of cavity quantum electrodynamics 1,2 has been reached for real atoms in optical cavities 3 , and for artificial atoms in circuit quantum electrodynamics 4 and quantum dot systems 5,6 . A signature of strong coupling is the splitting of the cavity transmission peak into a pair of resolvable peaks when a single resonant atom is placed inside the cavity, an effect known as vacuum Rabi splitting. The circuit quantum electrodynamics architecture is ideally suited for going beyond this linear-response effect. Here, we show that increasing the drive power results in two unique nonlinear features in the transmitted heterodyne signal: the supersplitting of each vacuum Rabi peak into a doublet and the appearance of extra peaks with the characteristic √ n spacing of the Jaynes-Cummings ladder. These findings constitute direct evidence for the coupling between the quantized microwave field and the anharmonic spectrum of a superconducting qubit acting as an artificial atom.Circuit quantum electrodynamics (QED) realizes the coupling between a superconducting qubit and the microwave field inside an on-chip transmission-line resonator 4,7 . The drastic reduction in mode volume for such a quasi-one-dimensional system 8,9 , the recent improvement in coherence times 10 and the absence of atomic motion render circuit QED an ideal system for studying the strong-coupling limit. In the customary linear-response measurement of the transmitted microwave radiation, the vacuum Rabi splitting manifests itself as an avoided crossing between the qubit and the resonator.It may be argued that the observation of the splitting is not yet a clear sign for quantum behaviour 11,12 , because avoided crossings are also ubiquitous in classical physics. However, quantum mechanics gives rise to a distinct anharmonicity of these splittings when initializing the resonator in a higher photon Fock state: when the resonator mode is occupied by n photons, the splitting is enhanced by a factor √ n + 1 as compared with the vacuum Rabi situation. This anharmonicity has been observed with single atoms in both microwave 13 and optical cavities 14,15 . In circuit QED, this characteristic trait has been observed in time-domain measurements 16 . In a system similar to ours, the position of the n = 2 peaks was recently demonstrated in a two-tone pump-probe measurement 17 .Here, we present a theoretical analysis and experimental investigation of the vacuum Rabi resonance in a circuit QED system, where we study the √ n anharmonicity up to n = 5 by exploring the power dependence of the heterodyne transmission (see the Methods section). This type of detection is particularly simple, because it is a continuous measurement involving only a single dr...

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confidence: 80%

Nonlinear response of the vacuum Rabi resonance

et al. 2008

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“…Two advantages of superconducting qubit architectures are the use of conventional microfabrication techniques, which allow straightforward scaling to large numbers of qubits, and a toolkit of circuit elements that can be used to engineer a variety of qubit types and interactions [6,7]. Using a number of recent qubit control and hardware advances [7][8][9][10][11][12][13], here we demonstrate a nine-quantum-element solid-state QuP and show three experiments to highlight its capabilities. We begin by characterizing the device with spectroscopy.…”

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confidence: 99%

“…We begin by characterizing the device with spectroscopy. Next, we produces coherent interactions between five qubits and verify bi-and tripartite entanglement via quantum state tomography (QST) [8,12,14,15]. In the final experiment, we run a three-qubit compiled version of Shor's algorithm to factor the number 15, and successfully find the prime factors 48 % of the time.…”

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confidence: 99%

Computing prime factors with a Josephson phase qubit quantum processor

et al. 2012

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A quantum processor (QuP) can be used to exploit quantum mechanics to find the prime factors of composite numbers [1]. Compiled versions of Shor's algorithm have been demonstrated on ensemble quantum systems [2] and photonic systems [3][4][5], however this has yet to be shown using solid state quantum bits (qubits). Two advantages of superconducting qubit architectures are the use of conventional microfabrication techniques, which allow straightforward scaling to large numbers of qubits, and a toolkit of circuit elements that can be used to engineer a variety of qubit types and interactions [6,7]. Using a number of recent qubit control and hardware advances [7][8][9][10][11][12][13], here we demonstrate a nine-quantum-element solid-state QuP and show three experiments to highlight its capabilities. We begin by characterizing the device with spectroscopy. Next, we produces coherent interactions between five qubits and verify bi-and tripartite entanglement via quantum state tomography (QST) [8,12,14,15]. In the final experiment, we run a three-qubit compiled version of Shor's algorithm to factor the number 15, and successfully find the prime factors 48 % of the time. Improvements in the superconducting qubit coherence times and more complex circuits should provide the resources necessary to factor larger composite numbers and run more intricate quantum algorithms.In this experiment, we scaled-up from an architecture initially implemented with two qubits and three resonators [7] to a nine-element quantum processor (QuP) capable of realizing rapid entanglement and a compiled version of Shor's algorithm. The device is composed of four phase qubits and five superconducting coplanar waveguide (CPW) resonators, where the resonators are used as qubits by accessing only the two lowest levels. Four of the five CPWs can be used as quantum memory elements as in Ref. [7] and the fifth can be used to mediate entangling operations.The QuP can create entanglement and execute quantum circuits [16,17] with high-fidelity single-qubit gates (X, Y , Z, and H), [18,19]combined with swaps and controlled-phase (C φ ) gates [7,13,20], where one qubit interacts with a resonator at a time. The QuP can also utilize "fast-entangling logic" by bringing all participating qubits on resonance with the resonator at the same time to generate simultaneous entanglement [21]. At present, this combination of entangling capabilities has not been demonstrated on a single device. Previous examples have shown: spectroscopic evidence of the increased coupling for up to three qubits coupled to a resonator [14], as well as coherent interactions between two and three qubits with a resonator [12], although these lacked tomographic evidence of entanglement.Here we show coherent interactions for up to four qubits with a resonator and verify genuine bi-and tripartite entanglement including Bell [9] and |W -states [10] with quantum state tomography (QST). This QuP has the further advantage of creating entanglement at a rate more than twice that of previous demonst...

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“…The additional circuit-QED system (qubit and microwave cavity) allows both the deterministic preparation of the cavity in a single Fock state 26,[36][37][38] , and the dispersive QND readout of its population dynamics 25 . Thus in reality our proposed opto-electro-mechanical system is a circuit-QED-mechanical system, where the additional qubit-cavity part is used for state preparation and readout.…”

Section: Qnd Readoutmentioning

confidence: 99%