D-Wave Systems Inc. D-Wave Systems Inc. THE QUANTUM COMPUTING COMPANYTM A.M. Zagoskin (D-Wave Systems and UBC) A.Yu. Smirnov (D-Wave Systems) M.H.S. Amin (D-Wave Systems) Alec Maassen van den Brink (D-Wave Systems) E. Il’ichev (IPHT) A. Izmalkov (IPHT) M. Grajčar (Comenius University) Th. Wagner (IPHT) H.-G. Meyer (IPHT) Evidence for entangled states formation in a system of two coupled flux qubits Quantum Condensed Matter Meeting, Vancouver, January 2004

D-Wave Systems Inc. 3JJ flux qubit Orlando et al. (1999); van der Wal et al. (2000)

D-Wave Systems Inc. 3JJ flux qubit

D-Wave Systems Inc. Coupled 3JJ flux qubits Majer et al. (2003) Izmalkov et al. (2003)

Current experimental status of two-qubit entanglement D-Wave Systems Inc. Current experimental status of two-qubit entanglement NEC (!) - charge qubits Pashkin et al., Nature 421, 823 (2003) Yamamoto et al., Nature 425, 941 (2003) Maryland - CBJJ qubits Berkley et al., Science 300, 1548 (2003) Delft (?) - 3JJ qubits Majer et al., cond-mat/0308192 (2003)

Impedance Measurement Technique D-Wave Systems Inc. Impedance Measurement Technique Greenberg et al. (2002)

Impedance Measurement Technique D-Wave Systems Inc. Impedance Measurement Technique Voltage-current angle in the tank tan 

Coherent tunneling in a 3JJ qubit: IMT dip D-Wave Systems Inc. Coherent tunneling in a 3JJ qubit: IMT dip Voltage-current angle in the tank: solid line is a fit for /h = 650 MHz 

3JJ flux qubit coupled to a tank circuit D-Wave Systems Inc. 3JJ flux qubit coupled to a tank circuit Nb coil is prepared on oxidized Si substrates lithographically. The line width of the coil windings was 2 m, with a 2 m spacing. Various square-shape coils with between 20 and 150 m windings were designed. External capacitance CT.

D-Wave Systems Inc. Rabi spectroscopy M L C h  T Il’ichev et al. (2003)

The voltage spectral density at different HF amplitudes D-Wave Systems Inc. The voltage spectral density at different HF amplitudes at f=868  2 MHz

Fit to the experimental data D-Wave Systems Inc. Fit to the experimental data

Two qubits inductively coupled to a resonance tank D-Wave Systems Inc. Two qubits inductively coupled to a resonance tank Sq = 80 m2 Lq = 39 pH Ic  400 nA EC  3.2 GHz Mab = 2.7 pH CT = 470 pF LT  130 nH fT = 20.139 MHz QT = 1680 (at 10 mK) Izmalkov et al., cond-mat/0312332 (2003)

Two qubits inductively coupled to a resonance tank D-Wave Systems Inc. Two qubits inductively coupled to a resonance tank Izmalkov et al. (2003)

Two qubits inductively coupled to a resonance tank D-Wave Systems Inc. Two qubits inductively coupled to a resonance tank tan   -2 (QT/LT) (T) Izmalkov et al. (2003)

Signature of entanglement D-Wave Systems Inc. Signature of entanglement Izmalkov et al. (2003); Smirnov, cond-mat/0312635 (2003)

D-Wave Systems Inc. IMT dips (experiment) T = 10 (nominally), 50, 90, 160 mK Izmalkov et al. (2003)

D-Wave Systems Inc. IMT dips (theory) IMT deficit T = 50, 90, 160 mK Izmalkov et al. (2003)

Temperature dependence of IMT dips D-Wave Systems Inc. Temperature dependence of IMT dips Squares: qubit a, triangles: qubit b, circles: coincident Izmalkov et al. (2003)

Experimentally determined parameters D-Wave Systems Inc. Experimentally determined parameters a = 550 MHz b = 450 MHz Ia  Ib = Ip = 320 nA J = 420 MHz Izmalkov et al. (2003)

Measure of entanglement D-Wave Systems Inc. Measure of entanglement Concurrence at the co-degeneracy point: C1 = C4 = 0.39 C2 = C3 = 0.97 For the equilibrium density matrix at 10 mK Ceq = 0.33 Izmalkov et al. (2003)

D-Wave Systems Inc. Conclusions: IMT approach allows to observe the signature of entanglement in two coupled flux qubits Quantitative agreement between the theory and experiment confirms that the system is in an equilibrium mixture of entangled two-qubit states The quantitative measure of entanglement can be calculated Only a lower limit on the appropriate coherence time can be established Rabi spectroscopy experiments on two qubits are under way