Entanglement in a 20-Qubit Superconducting Quantum Computer

Mooney, Gary J.; Hill, Charles D.; Hollenberg, Lloyd C. L.

doi:10.1038/s41598-019-49805-7

Cited by 113 publications

(85 citation statements)

References 56 publications

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“…There are some indicators to evaluate the performance of a quantum computer, for example, negativity, 26 quantum volume, 27 or Mermin's inequalities 2 . However, the major difference between classical physics and quantum physics mainly is still mainly the entanglement property.…”

Section: Theorymentioning

confidence: 99%

Mermin's inequalities of multiple qubits with orthogonal measurements onIBMQ 53‐qubit system

Huang

Chien

Cho

et al. 2020

Quantum Engineering

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Summary Entanglement properties of IBM Q 53‐qubit quantum computer are carefully examined with the noisy intermediate‐scale quantum technology. We study Greenberger‐Horne‐Zeilinger‐like states with multiple qubits (N = 2 to N = 7) on IBM Rochester and compare their maximal violation values of Mermin's polynomials with analytic results. A rule of N‐qubits orthogonal measurements is taken to further justify the entanglement less than maximal values of local realism. The orthogonality of measurements is another reliable criterion for entanglement except the maximal values of LR. Our results indicate that the entanglement of IBM 53 qubits is reasonably good when N ≤ 4, while for the longer entangle chains, the entanglement is only valid for some special connectivity.

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Section: Theorymentioning

confidence: 99%

Mermin's inequalities of multiple qubits with orthogonal measurements onIBMQ 53‐qubit system

Huang

Chien

Cho

et al. 2020

Quantum Engineering

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“…One just needs to sum up the outcomes j in Eq. (14) for the multi-outcome scenario considered in that work. Our additional derivation of a weaker bound in Eq.…”

Section: Modifying the Quantum Witness For Clumsy Measurementsmentioning

confidence: 99%

“…The availability of public quantum computers, like the 'IBM quantum experience' (IBM QE) 1 , promises both applications [2][3][4][5][6][7][8][9][10][11] and tests of fundamental physics [12][13][14] . In particular, as the number of available qubits increases, it potentially allows for a rigorous study of the crossover between classical and quantum worlds 15,16 , including tests like the Leggett-Garg inequality (LGI) 17,18 .…”

Section: Introductionmentioning

confidence: 99%

Experimental test of non-macrorealistic cat states in the cloud

Lambert

Chan

et al. 2020

npj Quantum Inf

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The Leggett–Garg inequality attempts to classify experimental outcomes as arising from one of two possible classes of physical theories: those described by macrorealism (which obey our intuition about how the macroscopic classical world behaves) and those that are not (e.g., quantum theory). The development of cloud-based quantum computing devices enables us to explore the limits of macrorealism. In particular, here we take advantage of the properties of the programmable nature of the IBM quantum experience to observe the violation of the Leggett–Garg inequality (in the form of a ‘quantum witness’) as a function of the number of constituent systems (qubits), while simultaneously maximizing the ‘disconnectivity’, a potential measure of macroscopicity, between constituents. Our results show that two- and four-qubit ‘cat states’ (which have large disconnectivity) are seen to violate the inequality, and hence can be classified as non-macrorealistic. In contrast, a six-qubit cat state does not violate the ‘quantum witness’ beyond a so-called clumsy invasive-measurement bound, and thus is compatible with ‘clumsy macrorealism’. As a comparison, we also consider un-entangled product states with n = 2, 3, 4 and 6 qubits, in which the disconnectivity is low.

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“…This is due to the fact that in reality, quantum computers require more than three qubits to access data during high capacity information transmission. It is shown in the current recent, 20 qubits [1] and 50 qubits have been built and tested by IBM [2]. Throughout the time of entanglement concept's emergence, scientists initially rejected the idea because they were not convinced that entanglement could solve computer problem involving numerous data.…”

Section: Introductionmentioning

confidence: 99%

Entanglement Classification for a Three-qubit System using Special Unitary Groups, SU(2) and SU(4)

Mohd

Idrus

Zainuddin

et al. 2019

IJACSA

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Entanglement is a physical phenomenon that links a pair, or a set of particles that correlates with each other, regardless of the distance between them. Recent researches conducted on entanglement are mostly focused on measurement and classification in multiqubit systems. Classification of two qubits will only distinguish the quantum state as either separable or entangled, and it can be done by measurement. Meanwhile, in a three-qubit system, it becomes more complex because of the structure of the three qubits itself. It is not sufficient to do measurement because the states are divided into three types, including fully separable state, biseparable state, and genuine entangled state. Therefore, the classification is needed to distinguish the type of states in the three-qubit system. This study aims to classify the entanglement of three-qubit pure states using a combination model of special unitary groups, SU(2) and SU(4), by changing the angle of selected parameters in SU(4) and acting on the separable pure state. The matrix represents SU(2) is matrix while matrix for SU(4) is 4 matrix. Hence, the combination of SU(2) and SU(4) represent 8 matrix. This classification uses the von Neumann entropy and three tangle measurements to classify the class, respectively. The results of this study have indicated that the three-qubit pure state has been successfully classified into different classes, namely, A-B-C, A-BC, CAB , GHZ, and W, with A-B-C being a fully separable state, A-BC and CAB are biseparable states, and GHZ and W are genuine entangled states. The results show that this model can change separable pure states to other entanglement class after transformation is done.

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Entanglement in a 20-Qubit Superconducting Quantum Computer

Cited by 113 publications

References 56 publications

Mermin's inequalities of multiple qubits with orthogonal measurements onIBMQ 53‐qubit system

Mermin's inequalities of multiple qubits with orthogonal measurements onIBMQ 53‐qubit system

Experimental test of non-macrorealistic cat states in the cloud

Entanglement Classification for a Three-qubit System using Special Unitary Groups, SU(2) and SU(4)

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