REALIZING QUANTUM MEASUREMENTS WITH SUPERCONDUCTING NANOCIRCUITS

Transcription

1 REALIZING QUANTUM MEASUREMENTS WITH SUPERCONDUCTING NANOCIRCUITS IRFAN SIDDIQI YALE UNIVERSITY R. Vijay P. Hyafil E. Boaknin M. Metcalfe F. Pierre L. Frunzio C.M. Wilson C. Rigetti V. Manucharyan J. Gambetta R.J. Schoelkopf S.M. Girvin D.E. Prober M.H. Devoret Quantum Nanoelectronics Laboratory University of California, Berkeley ISCP Islamabad March UC BERKELEY K. Mai O. Naaman (NIST) K.G. Ray Z. Zibrat S. Onishi M. Sarovar D. Slichter K.Eid (Penn State) A. Zettl J. Clarke J. Long K.B. Whaley

2 CLASSICAL vs. QUANTUM INFORMATION classical equilibrium states quantum energy levels Energy } Ψ = α 0 + β OR 1 0> AND 1>

3 QUANTUM COHERENT MACHINES: MIRACLE or MIRAGE? N = 1 ATOM QUANTUM N = 10 5 QUANTUM COMPUTER COMPLEXITY N > OSCILLOSCOPE CLASSICAL ENTANGLE 10 5 QUANTUM OBJECTS TECHNOLOGICALLY FEASIBLE? FUNDAMENTALLY ALLOWED?

4 QUANTUM REALITY? There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature. -N. Bohr

5 QUANTUM MEASUREMENT PARADOX ATOM METER., ENV, or Can we fully control the measurement process? if yes, how macroscopic can we make the meter?

6 CHOSING AN ATOM : QUANTUM BITS Nuclear Magnetic Resonance Trapped Ions Superconducting Circuits 1μm (IBM/MIT) (NIST) (YALE) Advantages Challenges strong atom/meter coupling engineered atoms quantum electrical circuits decoherence readout

7 HOW CAN WE MAKE A CIRCUIT ATOM-LIKE? 1μm? 1> 0> Electrical Circuit Artificial Atom

8 HOW CAN A SUPERCONDUCTING CIRCUIT BECOME QUANTUM-MECHANICAL AT THE LEVEL OF CURRENTS AND VOLTAGES? SIMPLEST EXAMPLE: SUPERCONDUCTING LC OSCILLATOR CIRCUIT ALUMINUM MICROFABRICATION L ~ 3nH, C ~ 10pF, ω r /2π ~ 1GHz

9 LC OSCILLATOR AS A QUANTUM CIRCUIT φ +q -q V E I hω r [ ] φ, q = ih φ = LI q = CV φ SUPERCONDUCTING ELIMINATE DISSIPATIVE ENVIRONMENT

10 LC OSCILLATOR AS A QUANTUM CIRCUIT φ +q E -q V I hω r [ ] φ, q = ih φ = LI q = CV 1GHz hω > r kt B φ 10mK

11 LC OSCILLATOR AS A QUANTUM CIRCUIT φ +q -q V E I hω r [ ] φ, q = ih φ CANNOT STEER THE SYSTEM TO AN ARBITRARY STATE

12 THE JOSEPHSON TUNNEL JUNCTION: NON-LINEARITY AT ITS FINEST! δ I 0 I( δ ) = I sin( δ ) 0 (NON-LINEAR INDUCTOR) U( δ ) = h I0 cos( δ ) 2e

13 VARY LEVEL SPACING USING CHARGE & FLUX island U Φ island ˆ Φ H = E nˆ e E 2 4 c( Cg /2 ) 2 jcos cos 2ϕ 0 ˆ δ

14 SPLIT COOPER-PAIR BOX: TUNABLE ATOM U Φ E 1 hω 01 E/4E c Φ/Φ 0 E 0 C g U / 2e

15 DISPERSIVE QUANTUM MEASUREMENT YALE SPIN 1/2 couple YALE OSCILLATOR 10 μm JPL 1 hω 1 0 hω 0

16 NON-LINEAR INDUCTIVE READOUT: QUANTRONIUM write JJ=non-linear inductor U Φ read island

17 THE NON-LINEAR JOSEPHSON OSCILLATOR δ phase difference S S I 0 C I( δ ) = I sin( δ ) Vt () = h d ( ) 2edt δ U( δ ) = h I0 cos( δ ) 2e 0 L J ω P Nonlinear Oscillator Vt () 1 1 = = h di 2eI0 cos( δ ) dt 1 = LC J

18 THE JOSEPHSON ELECTRICAL PENDULUM: Non-linearity with minimal friction l θ ω 0 = g l L I l J C ω p 1 0 g ω 1 0 PENDULUM CLOCK (Galileo, ca. 1600) δ θ δ phase difference S S I 0 ω = JOSEPHSON JUNCTIONJ P C 1 LC ω p /2π ~ 1-10 GHz Non-linear & Non-dissipative Quantum Regime ( hω >>kt) P B

19 PERIODIC DRIVE U( h I0 /2 e) Ω I() t = i sin( Ωt) RF 2 4 h δ δ U( δ ) = I e 2 12 linear inductance non-linear inductance Ω two dynamical (Floquet) states δ max 0.25 IS et al., PRL (2005)

20 JOSEPHSON BIFURCATION AMPLIFIER i sin( Ω t+ φ) RF Z0 = R= 50Ω irf sin( Ωt) JBA: INPUT COUPLES TO I 0 - φ (i rf,i 0 ) - no on-chip dissipation - only fluctuations from R (minimal backaction) IS et al., PRL (2004)

21 COMBINING HIGH SENSITIVITY & SPEED LINEAR OSCILLATOR NON-LINEAR OSCILLATOR Q sets sensitivity kt sets sensitivity!

22 NATURE S BIFURCATION AMPLIFIER

23 MICROWAVE QUANTUM EAR nm mk GHz

24 ELECTRON BEAM LITHOGRAPHY IMAGING: < 1 nm WRITING: ~ 10 nm 10 cm

25 LIQUID HELIUM FREE COOLING in 24 hrs! 300 K 77 K 4.2 K 800 mk 100 mk 7 mk

26 ISOLATED POWER, ETC

27 Filters, Filters, and more Filters

28 RF BIASED JUNCTION: PHASE DIAGRAM irf sin( Ωt) 1/kT VDC (nv) i sin( Ω t+ φ) RF P ~ 0.1 fw 1/Q Q=ω p RC Ω Ω

29 QUANTRONIUM with BIFURCATION READOUT QUBIT CONTROL PULSE SEQUENCE (~ 20 GHz) QUBIT STATE ENCODED IN REFL. PULSE PHASE φ A 1 0 A i RF / I 0 READOUT PROBING PULSE (~ 1 GHz)

30 1 RABI OSCILLATIONS million measurements ~ 10 min (dead time ~0.2 sec) IS et al., PRB (2006)

31 1 RAMSEY FRINGES Δt

32 SINGLE MOLECULE MAGNET QUBIT CNT Weak Links (K. Ray) Cr 7 Ni (S=1/2) [(cyclen) 12 Ni 13 Cr 6 (CN) 36 ] 8+ (S = 22) [Mn 19 O 8 (N 3 ) 8 (HL) 12 (MeCN) 6 ] 2+ (S=83/2) measure spin state in ns strong magnetic coupling Metal Weak Links (K. Eid)

33 DRIVEN PENDULUM IN THE QUANTUM REGIME

34 cable elevator T = hx& 2 B π kc X & THE UNRUH EFFECT

35 HEAT WITHOUT FRICTION: THE DYNAMIC CASIMIR EFFECT Shaking Light from the Void Paul Davies Nature, News & Views, , 1996

36 HEAT WITHOUT FRICTION: THE DYNAMIC CASIMIR EFFECT T X kc 2 = hωδ B ΔXωr c F Lambrecht, Jaekel, and Reynaud PRL 77, 615 (1996) ΔX ΔL eff Ω hω F, ~1 T ~ r ~100mK ω k r B

37 QUANTUM ACTIVATION measure Γ Γ Τ esc T eff = n hω k B

38 SCHRÖDINGER'S CATS and KITTENS

39 MACROSCOPIC QUANTUM ERASURE atom meter photons or φ=0 φ=π prepare atom in superposition + send photons, entangle meter with atom φ=0 + φ=π photons arrive at classical readout + send detect pulse back (usual to atom/meter qubit readout) or + photons arrive at meter φ=0 + φ=π atom recovers original superposition +

40 LIMITS OF SUPERPOSITION? size Macroscopic Quantum Coherence MACROSCOPIC engineered Giant Macroscopic Quantum Coherence Does it exist? action-distance >> h p 2 hmω 100h 1 MQC~ 1 h h action distance quantum optics Schrödinger "lean" cat states ~ 10 JBA states ~ 100 ("fat" cat) 0 h xx m ω 22h h h

41 CONCLUSIONS SUPERCONDUCTING QUBIT READOUT DISPERSIVE: NO ENERGY LEFT BEHIND FAST: MEASURE 30ns, RECORD 100ns MINIMAL DEAD TIME: REPETITION RATE SET BY T 1 NON-INVASIVE: CAN TURN READOUT OFF PHYSICS QUESTIONS DECOHERENCE IN MANY-BODY QUANTUM SYSTEMS COHERENCE TIMES IN SINGLE MOLECULES/NANOTUBES AMPLIFY QUANTUM INFORMATION? FUNDAMENTAL LIMITS TO QUANTUM COMPLEXITY? THE QUANTUM PENDULUM DYNAMICAL CASIMIR EFFECT

42 DRIVEN PENDULUM: ALL T! U( h I0 /2 e) Ω U( h I0 /2 e) Ω low amplitude state high amplitude state quasi-energy (M. Dykman) ω Γ = exp 0 1 2π dyn dyn a ΔU kt Non-equilibrium quantum system Drive: Virtual vacuum fluctuations real photons switching

43 k B T<<hω: QUANTUM ACTIVATION equilibrium case only relaxation δ 4 ~ (a+a ) 4 ; χ 3 process, four wave mixing convert vacuum fluctuations into thermal fluctuations drive escape

44 DC CURRENT BIAS: Macroscopic Quantum Tunneling (MQT) Martinis et al, PRB 35 (1987) thermal activation hω ΔU * T > T = p kt : Γ e 7.2k MQT T hω * p < T = Γ= 7.2k : constant

45 CAN COOL JUNCTION & ENVIRONMENT cool R to mk; >1 GHz RF bandwidth T * hω p = = 5 15mK 7.2k

46 QUANTUM ACTIVATION VS. MQT SATURATION TEMPERATURE T T MQT QA = = 7.2k hω 2k hω B p B

47 CONCLUSIONS QUANTUM STATE READOUT DISPERSIVE: NO ENERGY LEFT BEHIND FAST: MEASURE 30ns, RECORD 100ns, NO DEAD TIME NON-INVASIVE: CAN TURN READOUT OFF OBSERVATION OF THE DYNAMIC CASIMIR EFFECT PERSPECTIVES COHERENCE TIMES IN SINGLE MOLECULES/NANOTUBES DECOHERENCE IN MANY-BODY QUANTUM SYSTEMS FUNDAMENTAL LIMITS TO QUANTUM COMPLEXITY?