Chiral groundstate currents of interacting photons

in a synthetic magnetic field

Pedram Roushan

Google Inc., Santa Barbara

Chania, June 2016 arXiv: 1606.00077

Prof. J. Martinis

Charles Neill Michael Fang (now Caltech)

Collaboration:

Prof. Eliot Kapit

Google quantum artificial intelligence team

Anthony Megrant Andrew Dunsworth

Dr. Hartmut Neven

Los Angele theory team:

Santa Barbara Hardware team:

… it is not going to work

Classical processor :

Computational power ~ linearly with

speed, RAM size, …

State of the art: < 40 interacting spins

Classical vs. quantum computer

Parallel processing of 23=8 states 3 qubits

doubling the power: n Qubits n+1 qubits

Quantum processor :

Computational power ~ exponential with

number of qubits

?

A quantum for a quantum

“Nature isn't classical, dammit, and if you want to make a simulation of

nature, you'd better make it quantum mechanical, and by golly it's a

wonderful problem, because it doesn't look so easy.”

-- Richard Feynman (1981)

Feynman, Int. J. Theor. Phys. (1982),

Lloyd, Science (1996)

Buluta & Nori, Science (2009)

…

Digital simulator

Analog simulator Let nature calculate for us !

Myths about quantum processor

1) Quantum platforms that need cryogenics

are not futuristic

2) Neutrino-ised qubits

for gaining longer

coherence times

3) There is nothing interesting to

do without error correction

4) We need exponential speed-up

Engineering platforms Spin qubits Ultra-cold atoms Trapped ions

Many body physics Long coherence, Room temp., Solid state

To

yli, e

t al., N

ano

Lett. 2

01

0

High fidelity logic gates

Mo

nro

e, e

t al., S

cie

nce

20

13

Blo

ch, N

atu

re P

hysic

s (2

00

5)

Superconducting circuits

Scalability

Contr

olla

bili

ty Full fledged

quantum simulator

Conventional experiment +

while maintaining coherence

)ˆcos()2/(

2

ˆ 2

0

2

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QH

..ohH intH

Barends et al., Nature (2014), Kelly et al. Nature (2015), Chen et al., PRL (2014), Roushan et al., Nature (2014)

)(

ˆˆ2

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hop

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...)2ˆ)(1ˆ(ˆ6

)1ˆ(ˆ2

)2/1ˆ(2

32

0..

nnnU

nnU

H

nH

int

oh RWA

RWA

The gmon architecture

A homebuilt variometer

)2

1(

)2

1(

02

01

q

q

L

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CCP LL

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)cos(2

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Many-body phases in interacting bosons

A holistic task:

1) Strong interactions

2) Synthetic gauge fields

3) Engineering flat band structure

Many-body physics

1) Fermionic systems

2) Bosonic systems

?

Fundamental

physics

Topological

computation

Theory and experiments so far…

A. Petrescu et al., PRA (2012)

J. Koch et al. , PRA (2010)

A. Nunnenkamp et al., New J. of Physics (2011)

A. L. C. Hayward et al. , PRL (2012)

M. Hafezi et al., PRB (2014)

E. Kapit et al., PRX (2014)

Superconducting qubits

J. R. Abo-Shaeer et al., Science (2001)

B. Paredes et al., Solid State communication (2003)

A. L. C. Hayward et al., PRL (2008)

J. Cho et al., PRL (2008)

Y.-J. Lin et al., Nature (2009)

A. L. Fetter, RMP (2009)

M. Aidelsburger et al., PRL (2013)

V. Schweikhard et al., PRL (2014)

H. Miyake et al., PRL (2013)

G. Jotzu et al., Nature (2014)

M. Hafezi et al., Nature Photonics (2013)

M. Rechtsman et al., Nature (2013)

L. Lu et al., Nature Photonics (2014)

L. Tzuang et al., Nature Photonics (2014)

J. Ningyuan et al., PRX (2015)

S. Raghu et al., PRA (2008)

Z. Wang et al., Nature (2009)

A. Khanikaev et al. Nature materials (2013)

D. Hugel et al., PRA (2014)

S. Kessler and F. Marquardt, Phys. Rev. A (2014)

M. Atala et al. ,Nature Physics (2014)

J. Flavin et al., PRX (2014)

Cold atoms and trapped ions

Fully controllable & coupled qubits

On and off resonance tunneling

33

))((2

)(ji

iiiiij

Z

i

i

i tgtH

modulating coupling terms

where,

, and if

Then, using RWA, the effective Hamiltonian becomes:

is gauge-invariant

Engineering complex hopping

Universal two-qubit interactions: E. Kapit, PRA (2015)

Pulse sequence In the lab:

Then, using RWA, the effective Hamiltonian becomes:

is gauge-invariant

Single photon circulation

Single photon circulation

)()(:)()(

)()(:

tTtTRStTtif

ttTRS

sTsT 2,15 21

Understanding decoherence and dephasing

J. K

och e

t al. , P

RA

(201

0)

Classical non-reciprocity

N. A. Estep et al., Nature Physics (2014)

J. Kerckhoff et al., Phys. Rev. Applied (2015)

K. Fang et al., Nature Photonics (2012)

K. Fang et al., PRB (2013)

Entanglement circulation

OR

Evolution of the density matrix

Signature of strong interacting photons

0010

0110

Signature of strong interacting photons

0010

0110

Signature of strong interacting photons

0010

0110

...)2ˆ)(1ˆ(ˆ6

)1ˆ(ˆ2

32 nnnU

nnU

H int MHzUU 22032

MHzg 50

3

0 )(2kj

kj

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kj

i

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0

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gg

egg

TtH

B

B

i

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)0(

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Ground state chirality

Adiabatic ramping

2ˆ 2121

21

Y

Q

X

Q

X

Q

Y

Q

QQI

t

nII

Qout

Q

in

Q

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i

t

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)(ˆ21

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21

12

21

QQ

i

QQ

i

QQ aaeaaeiI

define:

measure:

Chiral currents in groundstate

11.5 mm

An o

ptic

al m

icro

gra

ph o

f the 9

-qubit c

hip

.

At Google we are focusing on quantum computation

and

we are open to ideas

1,000$ vs. 1,000,000$

… …

Come and visit us at Santa Barbara !

UCSB lab

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