Construction of controlled-NOT gate based on microwave-activated phase (MAP) gate in two transmon system

We experimentally constructed an all-microwave scheme for the controlled-NOT (cNOT) gate between two superconducting transmon qubits in a three dimensional cavity. Our cNOT gate is based on the microwave-activated phase (MAP) gate, which requires an additional procedure to compensate the accumulated phases during the operation of the MAP gate. We applied Z-axis phase gates using microwave hyperbolic secant pulse on both qubits with adequate rotation angles systematically calibrated by separate measurements.We evaluated the gate performance of the constructed cNOT gate by performing two-qubit quantum process tomography (QPT). Finally, we present the experimental implementation of Deutsch-Jozsa algorithm using the cNOT gate

Study of microwave-activated c-Phase (MAP) gate in two transmon qubit system

We have studied two qubit MAP (microwave-activated c-Phase) gate demonstrated earlier by J. Chow et al.[1] in our 3D transmon qubit system. Instead of choosing two fixed-transition frequency qubits, we replaced one of them to a tunable-frequency qubit in order to precisely align the higher energy levels 03 and 12 in situ. This experimental set up led us to realize the ideal condition for implementing and optimizing MAP gate, where we explored the shortest gate time in this scheme. We will present the estimation of the fidelity of Bell states generated by MAP gate with tomographic reconstruction of the two-qubit states

Study on the squeezed microwave photon prepared by a Josephson parametric amplifier

Squeezed state is essential for detecting a weak signal with a reduced noise level. It can be prepared by using Josephson parametric amplifier (JPA) operating in the degenerate mode. We measured the gain by modulating the phase of local oscillator in homodyne setup and observed the gain level below the vacuum level indicating the formation of the squeezed state. Finally we reconstructed the quadrature tomographic histogram of the resulting squeezed state with Wigner function

Demonstration of Two-Qubit Algorithms in Superconducting Qubit System

Quantum computing platforms are expected to outperform their classical counterparts in solving certain technical problems such as factorization and searching process. With remarkable progresses in the field, a lot of efforts and attentions are being made to experimentally demonstrate such supremacy of quantum computation. As a primitive attempt, we have implemented simple and well-known two-qubit algorithms in our superconducting qubit system. Our system consists of two transmon qubits, one of which is a frequency-tunable qubit, embedded in a single copper cavity forming a circuit QED system. The entangling gate that is essential for implementing quantum algorithms has been realized by utilizing MAP (microwaveactivated phase) gate. We evaluate the performance of two-qubit processor by estimating the fidelity of the entangling gate with two-qubit quantum process tomography (QPT). Then we demonstrate the implementation of two-qubit algorithms such as Deutsch-Josza algorithm and Grover search

Implementation of Gate Set Tomography on Superconducting Transmon Qubit for Characterization and Optimization of Single Qubit Gates

Characterizing the fidelities of quantum gates and improving them are essential requirements to build a scalable quantum computation platform. Two typical methods for such purpose, i.e., randomized benchmarking and quantum process tomography, contain drawbacks that cannot be compensated without the aid of the other, which demands the development of a new stand-alone protocol. Gate set tomography (GST) is one of such protocols developed to obtain detailed information of qubit gates that are free from the state preparation and measurement (SPAM) errors. We have implemented GST on single transmon qubit embedded in a three dimensional cavity. As a result, GST analysis not only estimated the process matrices of target gates but also suggested the direction for further calibration to achieve more accurate gate operations

Qubit decoherence and the Purcell effect in 3D transmon qubit in circuit QED

In the current design of superconducting qubit based on circuit QED architecture, it can be rather challenging to place the resonant frequencies of all the qubits in ???strongly dispersive??? regime as the number of qubit increases for a practical purpose in future. Hence, we need to understand the qubit-photon interaction and its effect on the coherence of the qubit as the resonant frequency of a qubit approaches that of the cavity photon. In KRISS, we have made a series of measurements on a frequency-tunable transmon qubit embedded in a three dimensional cavity. As we tune the resonant frequency of the qubit towards that of the cavity, not only the diminishing of the coherence due to well-known Purcell effect near the resonance, but also a strong dependence of the coherence over a large range of frequency has been observed

Squeezing microwave photon using a Josephson parametric amplifier

The squeezed state is important to detect a weak signal with a low noise level and apply to the quantum entanglement. Josephson parametric amplifier (JPA) is a representative nonlinear resonator that can be used to generate the squeezed state in microwave frequencies. We fabricated the JPA consisting of LC resonator terminated with SQUID. The squeezed state is produced when the JPA operates in the degenerate mode, in which the pump frequency is twice the signal frequency. Here, we used the homodyne detection technique to characterize the generated squeezed state. Finally, we performed the tomographical reconstruction of the squeezed state by using the Wigner function