Implementing Deutsch-Jozsa algorithm using superconducting qubit network
Xiao-Hu Zheng
∗
,
1
Ming Yang,
1
Ping Dong,
1
and Zhuo-Liang Cao
†1
1
Key Laboratory of Opto-electronic Information Acquisition and Manipulation, Ministry of Education,
School of Physics and Material Science, Anhui University, Hefei, 230039, P R China
An improved architecture, which perform a universal set of gates by current biasing of coupling Josephson
junction, has been proposed. This improvement is necessary to the realization of a functional and scalable quan-
tum computer. The proposed architecture is in line with current technology. Secondly, we investigate a scheme
for implementing Deutsch-Jozsa algorithm via the improved architecture. It is a simple, scalable and feasi-
ble scheme for the implementation of Deutsch-Jozsa algorithm based on the current-controlled superconducing
charge qubit network.
PACS numbers: 03.67.Lx, 85.25.Cp
Keywords: Deutsch-Jozsa algorithm; Superconduction; Josephson charge qubits
Superposition principle of quantum state and entanglement
property make quantum computers possess potentially supe-
rior computing power over their classical counterparts, which
is demonstrated by some Quantum algorithms. Shor’s al-
gorithm [1] can be used to quickly factorize large numbers.
Grover search algorithm is fairly efficient in looking for one
item in an unsorted database of size N ≡ 2
n
[2, 3]. The
Deutsch-Jozsa (DJ) algorithm[4] is one of the simple quan-
tum algorithm which provides an exponential speed-up with
respect to classical algorithms. In this paper, we focus the DJ
algorithm.
The DJ algorithm can be briefly described as follows: As-
sume a Boolean functions f : {0, 1}
N
→ {0, 1}. If the func-
tion values are only single 0 or 1 for all 2
N
inputs, the func-
tion is called constant. If the function values are equal to 1
for half of all possible inputs, and to 0 for the other half, the
function is called balanced. The DJ algorithm is designed to
distinguish whether a function f is constant or balanced. With
a classical algorithm, this problem would, in the worst case,
require (2
N−1
+ 1) queries of f whereas the DJ algorithm re-
quires only one query by means of the following steps[5, 6],
as shown Fig. 1 (here we eliminate a 1-qubit function register
which is used for storing the function values , while retain an
N-qubit control register for the function arguments).
(i) N qubits are prepared in the initial state |00 . . . 0i.
(ii) Perform an N-qubit Hadamard transformation H
(iii) Apply the f-controlled phase shift U
f
|xi
U
f
−→ (−1)
f(x)
|xi , (x ∈ {0, 1}
N
) . (1)
(iv) Perform another Hadamard transformation H.
(v) Measure the final state. If the result is |00 . . . 0i the
function f is constant; if, however, the amplitude a
|00...0i
of
the state |00 . . . 0i is zero the function f is balanced. This is
because
a
|00...0i
=
1
2
N
X
x∈{0,1}
N
(−1)
f(x)
. (2)
∗
Electronic address: xhzheng@ahu.edu.cn
†
Electronic address:zlcao@ahu.edu.cn (Corresponding Author)
measure
final state
prepare
Initial state
f
U
H H
FIG. 1: Schematic diagram of the Deutsch-Jozsa
For realizing quantum computers, some physical systems,
such as nuclear magnetic resonance [7], trapped irons [8],
cavity quantum electrodynamics (QED) [9], and optical sys-
tems [10] have been proposed. These systems have the ad-
vantage of high quantum coherence, but can’t be integrated
easily to form large-scale circuits. Because of large-scale in-
tegration and relatively high quantum coherence, Josephson
charge qubit [11–13] and flux qubit [14, 15], which are based
on the macroscopic quantum effects in superconducting cir-
cuits [16, 17], are the promising candidates for quantum com-
puting. The DJ algorithm has special functions, so the imple-
mentation of DJ algorithm has become the focus of research.
For example, the DJ algorithm has been implemented with
pure coherent molecular superpositions [18], with quantum
dot [19, 20], and with cavity QED [21]. In this paper, we pro-
pose a physical scheme for implementing the DJ algorithm
with superconducting qubit network. It is a simple, scalable
and feasible scheme for implementing the DJ algorithm.
The paper is organized as follows: Firstly, we introduce
the structure and Hamiltonian of the current-controlled su-
perconducing charge qubit network. Secondly, we explain
how to implement a universal set of gates with this network.
Thirdly, we review the advantages, the decoherence feature
and extendability of the superconducting charge qubit net-
work. Fourthly, we illustrate the implementation of the DJ
algorithm. Finally, the conclusions are given.
Since the earliest Josephson charge qubit scheme [11] was
proposed, a series of improved schemes [12, 22, 23] have
been explored. Here, basing on the architecture of Joseph-
son charge qubit in Ref. [23], we propose an improved
architecture. The superconducting charge qubits structure
is shown in Fig.2. All N charge qubits (Q
1
, Q
2
, . . . , Q
N
)
can interact with the charge qubit Q
0
by a common large-
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