Quantum Computing with Superconductors I: Architectures

Geller, Michael R.; Pritchett, Emily; Sornborger, Andrew; Wilhelm, Frank K.

doi:10.1007/978-1-4020-6137-0_5

Cited by 19 publications

(16 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…entangling gate, the square root of i-SWAP (SQiSW) 8 , from which gates such as the CNOT can be constructed 9 . The SQiSW is a "natural" two-qubit gate as it directly results from capacitive coupling of superconducting qubits, yielding qubit coupling of the general form σ Ax σ Bx or σ Ay σ By , where σ x,y are the Pauli spin operators for qubits A and B 10,11 . Under the rotating wave approximation, the corresponding interaction Hamiltonian has the form ( ) .…”

mentioning

confidence: 99%

“…A more robust method is to compare the differences in tunneling of the first qubit caused by a change in tunneling of the second. From the four measurement probabilities P 00 , P 01 , P 10 , and P 11 , we extract for each qubit independent probabilities to be in the 1 state by "tracing out" the other qubit P 1A ≡ P 10 + P 11 P 1B ≡ P 01 + P 11 We measure P 1A (00) and P 1B (01) for the two cases where we prepare the initial states 00 and 01 , respectively. Using the correction matrices for X and F, we calculate ( )…”

mentioning

confidence: 99%

See 1 more Smart Citation

Quantum process tomography of a universal entangling gate implemented with Josephson phase qubits

et al. 2010

View full text Add to dashboard Cite

Quantum logic gates must perform properly when operating on their standard input basis states, as well as when operating on complex superpositions of these states.Experiments using superconducting qubits have validated the truth table for particular implementations of e.g. the controlled-NOT gate 1,2 , but have not fully characterized gate operation for arbitrary superpositions of input states. Here we demonstrate the use of quantum process tomography (QPT) 3,4 to fully characterize the performance of a universal entangling gate between two superconducting quantum bits. Process tomography permits complete gate analysis, but requires precise preparation of arbitrary input states, control over the subsequent qubit interaction, and simultaneous single-shot measurement of the output states. We use QPT to measure the fidelity of the entangling gate and to quantify the decoherence mechanisms affecting the gate performance. In addition to demonstrating a promising fidelity, our entangling gate has a on/off ratio of 300, a level of adjustable coupling that will become a requirement for future high-fidelity devices. This is the first solid-state demonstration of QPT in a two-qubit system, as solid-state process tomography has previously only been demonstrated with single qubits 5,6 .Universal quantum gates are the key elements in a quantum computer, as they provide the fundamental building blocks for encoding complex algorithms and operations. Single qubit rotations together with the two-qubit controlled-NOT (CNOT) are known to provide a universal set of gates 7 . Here, we present the complete characterization of a universal 2 entangling gate, the square root of i-SWAP (SQiSW) 8 , from which gates such as the CNOT can be constructed 9 . The SQiSW is a "natural" two-qubit gate as it directly results from capacitive coupling of superconducting qubits, yielding qubit coupling of the general form The amplitude of the swapping oscillations decreases with detuning as expected. In We fully characterize the SQiSW gate using quantum process tomography (QPT) 3,4 .This involves preparing the qubits in a spanning set of input basis states, operating with the gate on this set of states, and then performing complete state tomography on the output. As illustrated in Fig. 3a, we first perform quantum state tomography 15,17 on the input state 01 , which involves measuring the state along the x, y and z Bloch sphere axes of each qubit, in nine separate experiments. We then operate on the 01 input state with SQiSW, and perform complete state tomography on the output. These measurements allow for the evaluation of the two-qubit density matrix. This entire process is repeated 16 times in total, using four distinct input states for each qubit, chosen from the set ( )In Fig. 3b, we display the density matrix resulting from this tomography for the input state In a QPT experiment 18,19 errors arise from the entangling gate and errors in measurement. Since we are interested in the quality of the entangling gate itself, we have calibrated out er...

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

Quantum process tomography of a universal entangling gate implemented with Josephson phase qubits

et al. 2010

View full text Add to dashboard Cite

show abstract

“…The Feynman gate is a self-inverse gate, since x ⊕ (x ⊕ t) = t. Therefore, cascaded application of two Feynman gates acts as a two-qubit identity gate restoring the inputs at the outputs. The Feynman gate is a quantum realizable primitive gate [1,21,22]. The three-qubit Toffoli gate is shown in Fig.…”

Section: Reversible/quantum Gatesmentioning

confidence: 99%

Primitive quantum gate realizations of multiple-controlled Toffoli gates

Khan

2014

16th Int'l Conf. Computer and Information Technology

View full text Add to dashboard Cite

Multiple-controlled Toffoli gates are extensively used in quantum and reversible circuits. However, very limited attempt has been made for primitive quantum gate realizations of these gates. In this paper, we present realization of three-qubit Toffoli gate requiring five primitive quantum gates. We then propose realization of four-qubit Toffoli gate requiring 13 primitive quantum gates and one ancilla input. Finally, we propose realizations of (n + 1)- qubit (n > 3 control lines) Toffoli gates using (⎡n/2⎤ + 1)-qubit and (⎣n/2⎦ + 1)-qubit Toffoli gates and ancilla inputs, which make a trade off between quantum cost and number of ancilla inputs. Our proposed method outperforms the best result so far presented in the literature in terms of quantum cost and number of ancilla inputs.Index Terms-Multiple-controlled Toffoli gate, quantum circuit, quantum gate, realization of Toffoli gate, reversible circuit.

show abstract

“…Recent progress in superconducting artificial atoms [25][26][27] has made them appealing for quantum-information processing, especially for gate-based quantum computing [28]. An avoided-crossing-based CZ gate [29] has already been achieved for a system comprising coupled superconducting artificial atoms.…”

Section: Introductionmentioning

confidence: 99%

Designing High-Fidelity Single-Shot Three-Qubit Gates: A Machine-Learning Approach

2016

View full text Add to dashboard Cite

Three-qubit quantum gates are key ingredients for quantum error correction and quantum-information processing. We generate quantum-control procedures to design three types of three-qubit gates, namely Toffoli, controlled-NOT-NOT, and Fredkin gates. The design procedures are applicable to a system comprising three nearest-neighbor-coupled superconducting artificial atoms. For each three-qubit gate, the numerical simulation of the proposed scheme achieves 99.9% fidelity, which is an accepted threshold fidelity for fault-tolerant quantum computing. We test our procedure in the presence of decoherenceinduced noise and show its robustness against random external noise generated by the control electronics. The three-qubit gates are designed via the machine-learning algorithm called subspace-selective selfadaptive differential evolution.

show abstract

Quantum Computing with Superconductors I: Architectures

Abstract: Josephson junctions have demonstrated enormous potential as qubits for scalable quantum computing architectures. Here we discuss the current approaches for making multi-qubit circuits and performing quantum information processing with them.

Cited by 19 publications

References 42 publications

Quantum process tomography of a universal entangling gate implemented with Josephson phase qubits

Quantum process tomography of a universal entangling gate implemented with Josephson phase qubits

Primitive quantum gate realizations of multiple-controlled Toffoli gates

Designing High-Fidelity Single-Shot Three-Qubit Gates: A Machine-Learning Approach

Contact Info

Product

Resources

About