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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
q
QubitLC
QH
aan
aaiQ
aa
ˆ
)(ˆ
...)!6
ˆ
!4
ˆ
!2
ˆ1(
)2/(
2
ˆ 6422
0
2
q
QubitLC
QH
..ohH intH
Barends et al., Nature (2014), Kelly et al. Nature (2015), Chen et al., PRL (2014), Roushan et al., Nature (2014)
)(
ˆˆ2
212
kjkjhop
q
hop
aaaagH
L
MH
M RWA
...)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
M
L
M
2
12 g
I1 I2
CCP LL
MMM
2
21
M1 M2
Cq LLL
MMg
)cos(2
)cos(
2/
0
210
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
i
kj
i
eff aaeaaeg
H jkjk
0
0
0
)(
00
00
00
geg
gg
egg
TtH
B
B
i
i
Adiaeff
000
000
00
)0(
1
tH
1000 ?AdiaT
Ground state chirality
Adiabatic ramping
2ˆ 2121
21
Y
Q
X
Q
X
Q
Y
Q
QQI
t
nII
Qout
Q
in
Q
1
11
ˆˆˆ
]ˆ,ˆ[ˆ
1
1
Q
QnH
i
t
n
)(ˆ21
12
21
12
21
i
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
Google, Santa Barbara